Hi.
I just implemented $subj. I can't be sure all decisions I made are right, so I request a review. There are a couple of screen shots, for those who don't like applying patches: [1], [2].
In the first shot you can see I had to change the preferences dialog. I made it so that it would be possible to determine the preferable style of the marker (line/background) at any moment. There are some cases when it is necessary: for example, a user may disable the marker globally, but turn it on for particular project. With prev. version of the dialog we wouldn't be able to decide which marker style to use.
I did not make style and color settings project-specific intentionally, that would be just useless.
I had to tamper GeanyEditor struct a bit. It seems to cause no troubles for plugins as GeanyEditor is not exported. Fields 'long_line_*' are renamed to corresponding 'long_line_global_*' to emphasize they got different semantics.
[1] Preferences Dialog: http://xmages.net/upload/839ca662.png [2] Project Properties: http://xmages.net/upload/602c3e80.png
Best regards, Eugene.