Update path2regex (third time's the charm, hopefully.)

[Lord-Kamina]

I've corrected several errors in my port of the newer javascript code. Behavior should now be identical to path-regexp@6.2.0; and I've updated the test suite to reflect this.

There's still going to be breaking changes for some people, but they'll likely be things path-to-regexp itself already had a while ago. Not all of these have yet made it into express.js, though., given that the 5.0 betas depend on path-to-regexp 3.2.0

From documentation of path-to-regexp, main changes are (most are copied from the path-to-regexp release notes):

This time around, I tested it using C++14, and all tests were passing.

1. Allow empty string with ending: false to match both relative and absolute paths
2. Use delimiter when processing repeated matching groups (e.g. foo/bar has no prefix, but has a delimiter)
3. Support starting option to disable anchoring from beginning of the string
4. Various enhancements from path-to-regexp 6.0, which are intended partly to restore some compatibility with older versions:
   • Support for nested non-capturing groups in regexp, e.g. /(abc(?=d))
   • Support for custom prefix and suffix groups using /{abc(.*)def}
   • Tokens in an unexpected position will throw an error:
     • Paths like /test(foo previously worked treating ( as a literal character, now it expects ( to be closed and is treated as a group
     • You can escape the character for the previous behavior, e.g. /test\(foo
5. Support custom prefixes (same as delimiters in RESTinio) option (default is /. which acts like every version since 0.x again)
6. Add support for {} to capture prefix/suffix explicitly, enables custom use-cases like /:attr1{-:attr2}?
7. Use /#? as default (end)delimiter to avoid matching on query or fragment parameters; if you are matching non-paths (e.g. hostnames), you can set delimiterto .
8. Fix invalid matching of :name* parameter

I've updated the test suite to reflect the changes, as well as added some new tests that had been added to the upstream path-to-regexp as well.