Add DashedRoute class.

Checkout the demand for dashed urls in #4755 in :smile: 
Maybe `Inflector::camelize()` (and `Inflector::humanize()`) should get an parameter to specify the separator, or, just match `[_-\s]`, I have a feeling that the juggling between `-`, `_` and `' '` is becoming a bit messy.

This could be moved to a separate PR though, just something I noticed because of this PR