This commit goes a long way toward refactoring glob sets so that the
code is easier to maintain going forward. In particular, it makes the
literal optimizations that glob sets used a lot more structured and much
easier to extend. Tests have also been modified to include glob sets.
There's still a bit of polish work left to do before a release.
This also fixes the immediate issue where large gitignore files were
causing ripgrep to slow way down. While we don't technically fix it for
good, we're a lot better about reducing the number of regexes we
compile. In particular, if a gitignore file contains thousands of
patterns that can't be matched more simply using literals, then ripgrep
will slow down again. We could fix this for good by avoiding RegexSet if
the number of regexes grows too large.
Fixes#134.
