Migrate to mailgun/route package for routing

@r0mant @russjones can you please review? This change migrates Vulcan library to use mailgun/route library
Would not it be more beneficial to treat route expressions as trie by default, e.g. returning `Path(%v)`? This would let specify routes as just `/v2/<domain>/blah` and get all trie's speed benefits.

Also, why is it `%#v` and not just `%v`?