Add native support for UUIDs and dates (of varying formats) in switches.

[hgzimmerman]

Is your feature request related to a problem? Please describe.
UUIDs (& GUIDs), as well as Dates can appear in URL locations, but this library doesn't have any built in support for parsing those datatypes out of a route.

Describe the solution you'd like
UUID-like objects and Dates should have implementations of Switch, so users of this library don't need to newtype them in order to implement Switch for them themselves.

They should be feature-gated, and enabled by default.

I think the way they are parsed should be as permissively as possible, although dates probably won't aim to support mm/dd/yy because of the slashes.