Third release candidate for gnuplot 6

[Ethan A M. <me...@uw...>]

The "testing" directory on SourceForge now has a tarball for gnuplot-6-0-rc3

   https://sourceforge.net/projects/gnuplot/files/gnuplot/testing/gnuplot-6.0.rc3.tar.gz

This is a third release candidate for version 6.0.
Your feedback from testing of this release candidate will contribute to
the success of a full 6.0 release by the end of the year.

The most visible addition since rc2 is preliminary support for redrawing
or mousing complete multiplots.  The mousing part still has a lot of rough edges
so it is off by default but can be enabled by
	set mouse multiplot
The redraw previous multiplot part works well.  If gnuplot knows that the
immediately previous plot command was part of a multiplot, then "replot"
will redraw the full mulitplot.  If some other plot has intervened, then the
previous multiplot can still be recreated by "remultiplot".

Release Notes date:  13-Nov-2023

                Changes between 6.0-rc2 and -rc3
                ================================

- Replotting and mousing multiplots
        o new commands "remultiplot", "set mouse multiplot"
        o command sequence to regenerate full multiplot is saved to a datablock
- Additional keyentry options to construct custom keys
        o keyentry "text" can be used to place a secondary title in the key
- Minor fixes
        o correct build of postscript terminal when libgd and cairo are not present
        o strip trailing CR from function blocks read from a dos file
        o use 64-bit integers for iteration
        o "unset pointintervalbox" disables the box rather than setting it to default size
        o setting minitic scale to 0 does not disable the corresponding grid lines
        o use of stacked histograms with variable number of data columns

        Features introduced in version 6
        ================================
For a detailed list of new features, with illustrations, see
  http://gnuplot.info/docs_6.0/NewFeatures.html

For more example plots see
  http://gnuplot.info/demo_6.0/

  - Function blocks and scoped variables
  - Larger collection of special and complex-valued functions
  - New plot styles
        o 2D plot style `with surface` works in 2D polar coordinates to produce a
          solid-fill gridded representation of the plane. This is analogous to the
          use of dgrid3d and pm3d to produce a 3D gridded surface.
        o 2D plot style `with sectors` renders one annular segment ("sector") for
          each line of input data. This style can generate pie and donut charts,
          windrose charts, and a polar equivalent to sparse-matrix heatmaps.
        o 2D plot style `with lines` now has a filter option `sharpen`.
          This filter detects spikes in a function plot that would be missed or
          under-represented due to coarse sampling.  It adds an additional
          sampling point at the location of each such peak.
        o 3D plot style `with contourfill` produces 2D or 3D surfaces with
          distinct z-ranges indicated by solid color fill.
  - Hulls, masks, and smoothing
        o A cluster of 2D points can be replaced by a bounding polygon ("hull").
          Both convex hulls and concave hulls (χ-shapes) are supported.
        o Any hull or other closed path can be used as a mask to display only
          selected regions of a pm3d surface or image plot.
        o New smoothing option "smooth path" can be used on 2D and 3D curves
          that are not monotonic on x or y.  This allows smoothing of hulls.
  - Named palettes
        o The current palette can be saved to a named colormap for future us.
        o A predefined palette named "viridis" is provided.
        o Plots can specify a previously saved palette by name.
          This permits the use of multiple palettes in a single plot command.
        o Named palettes can be edited to contain an alpha channel.
  - New built-in functions and array operations
        o palette(z) returns the current RGB palette color mapping for z.
        o rgbcolor("name") returns the 32bit ARGB value for a named color.
        o index(Array, element) returns the first index i for which Array[i]
          is equal to element.
        o split("string", "separator") unpacks the fields in a string into
          an array of strings.
        o join(array, "separator") is the complement to split().
          It concatenates the elements of a string array into a single string.
        o `stats <non-existent file>` yields a testable value with no error;
          useful to avoid errors or warnings in scripts.
  - Program control flow
        o New syntax if {...} else if {...} else {...}
        o XDG base directory conventions for configuration files are supported.
        o `unset warnings` suppresses output of warning messages to the console.
        o The `fit` command is protected by exception handling. Control always
          returns to the next line of input even in the case of fit errors.
          On return FIT_ERROR is non-zero if an error occurred.
        o "Watchpoints"  are target values associated with individual plots
          in a graph. As that plot is drawn, each component line segment is
          monitored to see if its endpoints bracket the target value of a
          watchpoint coordinate (x, y, or z) or function f(x,y).
          If a match is found, the [x,y] coordinates of the match point are
          saved for later use.  Possible uses include
                - find the intersection points of two curves
                - find zeros of a function
                - find and notate where a dependent variable or function f(x,y)
                  crosses a threshold value
                - use the mouse to track values along multiple plots simultaneously
  - New terminals and terminal options
        o Terminals that display graphics in the same window as text entry now
          support pseudo-mousing; i.e. they respond to arrow keys and other
          hot-key bindings during "pause mouse".
        o New terminals kittygd and kittycairo provide in-window graphics for
          terminal emulators that support the kitty protocol.
        o New terminal webp generates a single frame or an animation sequence
          using webp encoding. Frames are generated using pngcairo,
          then encoded through the WebPAnimEncoder API.
        o New terminal block for text-mode pseudo-graphics uses Unicode block
          or Braille characters to offer improved resolution compared to the
          dumb or caca terminals.
        o latex terminals standalone mode updated to work with texlive2023
  - Miscellaneous other new features
        o Time unit settings for major and minor axis tics.  For example,
          minor tic marks can be placed at exactly one month intervals.
        o The character sequence $# in a using specifier evaluates to the total
          number of columns available in the current line of data.
          "plot FOO using 0:(column($# - 1))" plots the last-but-one field of each row.
        o keyword binvalue=avg plots the average, rather than the sum, of binned data.
        o "set colorbox bottom" places the color box underneath the plot.
        o "set pm3d spotlight" adds a user-controlled spotlight to the lighting model.
        o New key layout options to force specific width or number of columns.
          Automatic positioning of the key on the page can be manually tweaked
          by giving an offset.
        o "set isotropic" adjusts the axis scaling in both 2D and 3D plots such
          that x, y, and z axes all have the same scale.
        o Text rotation angles are not limited to integral degree values.
        o Data-driven color assignments in plot style "histograms".

	happy gnuplotting,

		Ethan