This feature "exports" the source code in the same format it appears
in on screen. The five columns on the left are optional, the four
on the right can be resized. Exported text can span the entire file
or just the current selection. Output can be plain text or CSV.
(I still haven't figured out a good use for CSV.)
The old copy-to-clipboard function is now implemented via the export
mechanism.
This adds a new clipboard mode that includes all columns. Potentially
useful for filing bug reports against SourceGen.
81157b6b47