This pull request's main intention is to wraps long strings (as requested by #182); however, it also provides better string handling in general and, in doing so, closes the following issues:
Closes#26Closes#182Closes#933Closes#1183Closes#1243
It turns out we also need to handle invisible *left* parens added at
the *start* of a line. Refactor `contains_unsplittable_type_ignore` to
handle this more cleanly.
In #1040 I had convinced myself that the type ignore logic didn't
need anything like the ignored_ids from the type comment logic, but I
was wrong, and we do.
We hit these cases in practice a bunch.
Type comments only apply if they are the first comment on the line,
which means that allowing them to be pushed behind a regular comment
when joining lines is a semantic change (and, indeed, one that black
catches and fails on).
