Added scheme mode.

Painter will now on every change first paint style buffer with default
style, then apply matched one. With this, things like erasing
characters to the state they are no longer recognized with the
matcher, will revert them to old color, not keep painted one.

Small changes in python-mode: comments are put to be matched last, so
matching engine does not paint keywords et al. inside comment
blocks. With this, no complexity is introduced in matching engine, but
can be confusing to users who does not understainds it. Maybe some
macro (e.g. 'define-mode') could reorder those statements?