Namespaced crypt package #2

This PR adds namespaces to all the Crypt\* classes and implements PSR-4 autoloading.

Squashed version.
> There is no reason for the class_exists check in the first place, because it would always exist, unless the file was deleted.

This is precesily the use case. Let's keep that for now.

> There needs to be a better mechanism to tell Random which crypto algorithm to use that doesn't require files to be deleted.

Possibly. Different story, though.