Add support for automatically disabling in certain syntax regions

[LunarWatcher]

This would essentially get rid of g:AutoPairsStringHandlingMode = 2, and make it generic. This should add a variable that defines syntax regions to ignore. If someone decides to include string and comment, auto-pairs shouldn't auto-complete in string or comments. This would also solve parts of #23

A minor caveat here, though, is that it's still beneficial if jumping in strings in particular still works. I.e. "some text|", " at | results in "some text"|, and not "some text"|". Of course, if no jump is available ("some |text", " at |), it should insert a single character ("some "|text")

This may or may not require #41 to be doable; merging to develop is preferred

[LunarWatcher]

Blocked by https://github.com/vim/vim/issues/8924 for now; synID and synstack aren't viable at a scale without adding group caching, and I just don't want to implement that when there might be better options on the way