nPlot 0.4.6 released

Changes:
* Fixed a very unpleasant bug causing nPlot to freeze if the data on X axis were orders of magnitude higher than the data on Y axis
* Added data reader and coordinate reader
* Added ability to plot data with error bars
* Added ability to import data with multiple columns
* Added nice icons for choosing TeX symbols in axes labels
* Changed window icon from ugly Times "n" to beautiful Computer Modern Math Italic "n" (unfortunately, it looks rather badly on Windows; maybe I'll change it in the next release)