relax SVN archive

Spin ids are no longer passed into write_xy_header().

Instead the new args seq_type and set_names are passed in.

Typo fix in write_xy_header().

axis_label should have been axis_labels!

Added the axis_min and axis_max args to write_xy_header() for specifying the graph ranges.

Fix for the call to write_xy_header().

This is now independent of the number of data sets, and is called correctly.

Deletion of the write_header() function.

This is now redundant due to the improvements in write_xy_header().

Added symbol formatting to the individual graph sets in write_xy_header().

Bug fix for write_xy_header(), a statement typo was stopping relax from running.

More changes to write_xy_header().

The return_units() and return_grace_string() analysis specific methods are no longer passed in as
args but are set up in the method itself. Many simplifications have been made. And now spin data
has been made axis independent - it can be X or Y data.

write_xy_header() now has a sets arg for specifying the number of data sets in the graph G0.

Clean up of write_xy_header().

Labels are now not overwritten if supplied, all file.write() operations are collected together, and
the X and Y-axis settings have been merged.