[Validator] New validator for UUIDs

This PR adds a new validator for [RFC 4122](http://tools.ietf.org/html/rfc4122)-compliant [universally unique identifiers (UUIDs)](https://en.wikipedia.org/wiki/Universally_unique_identifier).  This implementation validates both the format and (optionally) the UUID version.

Comments and feedback would be greatly appreciated :)

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | 
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | 

**TODOs:**

 - [ ] Gather feedback
 - [ ] Ensure all tests pass
 - [ ] Submit PR for the documentation