#2 Make [=[ ... ]=] and similar work (for both comments and strings)

It requires support specific to the syntax highlighter in question, so that's been added.

Here's a test case:

--[===[
xy]]=]===]==]z

As equal signs are removed on the top line, the part considered a comment should change.

(Edit: It seems that the built-in syntax highlighting of GOGS is not highlighting the above properly as of this writing.)

Force-pushed to revert an extra change that got committed by accident.