#2 Add line numbers to editor (and highlighting, code folding)

[Sebastian Schuberth]

This request is somewhat related to request 1593316,
which suggests to use wxWidgets for the UI. If that
would be done, one could easily use wxScintilla
(http://wxcode.sourceforge.net/components/wxscintilla/)
for the code editor, which would add line numbers,
syntax highlighting, code folding and more in a single
blow.

However, Scintilla (which wxScintilla is built upon)
does not depend on wxWidgets, so using Scintilla
(http://scintilla.sourceforge.net/) might be also of
interest when not porting to wxWidgets.