Edit comments

Revise based on recent changes to the symbol def topic.
> And btw, the TM_COMMENT_DISABLE_INDENT example block is wrong. It should also be mentioned that this is expected to be yes or no (strings).

Fixed.

> Edit: Actually, this entire section with TM_COMMENT_START and _END is kinda wrong now. You should read into comments.py.

Will check, but I don't think we should explain implementation details. I think the point is that `TM_COMMENT_START` should be used for line comments, and `TM_COMMENT_START[END]_2` should be used for block comments.

I don't think ST uses the comment.py code for anything else?