Namespace registered Faraday middleware

Just namespacing the code for a middleware in a module is, sadly, not
enough, as the name when you register it might clash with middleware
from other libraries that register the same type of middleware (for
example, the [Twitter ruby gem][1] registers a `:parse_json` middleware,
which provokes projects using both the twitter and diffbot gems to raise
an error when an error response comes back from twitter.

[1]: https://github.com/sferik/twitter
Merge pull request #2 from foca/namespace-faraday-middleware

Namespace registered Faraday middleware