Compilation error when parsing "[\\w-]+"

[Orvid]

A relatively common way to write a set that include a - character is to stick it at the end of the set, where it doesn't get parsed as a range, but instead as a literal -. CTRE currently fails to parse this. It does parse and work correctly if the - is manually escaped: "[\\w\\-]+"

[Orvid]

The same issue also applies to using an unescaped - as the first character in a set.

I've also discovered that some versions of RE2 have issues with escaped - characters in sets, which makes maintaining compatibility a bit harder.

Thankfully, while manually adding support for a trailing unescaped - in a set is a bit complicated (it's likely easier with access to desatomat), adding support for a leading unescaped - is much easier, a single line even :D I'll put up a PR for that here soon.