Add compatibility with rocket

[Louis]

Motivation
When using the web framework rocket it can be helpful to use the Uuid struct from this crate for user authentication. For that to work more easily it would be helpful if Uuid would implement the traits FromRequest and FromParam.

See #649

Solution
Add new feature called rocket that will enable the implementation of the traits FromRequest and FromParam for Uuid.

Alternatives
See #649

Is it blocking?
See #649

Anything else?
I'm implementing this feature and a pull request has already been opened #650.

[Louis]

Closing because this can already be archived by enabling the uuid feature inside rocket. See #650 for more information.