Add tests for how it should work

Some tests fail. Not sure what needs to change to make this work.

After closing quotes, it will keep adding quotes and not find the
preceding parens.

For some reason closing include strings fails. Possibly a different kind
of string syntax attribute.
Separate matched vs unmatched pairs

Reduce the duplication of the pair characters by separating the two
types into dicts that we can join into text classes.
Add support for angle brackets
Refactor synIDattr into is_string
Junk: Try to make string checking optional

Trying to be able to flip to the original (stackoverflow)
implementation, but I'm missing something because it doesn't work.