Add Gemspec

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

Namespace registered Faraday middleware

One of the code blocks appeared to have been missed :)

Add missing syntax highlighting to README

Fix that timeouts try to raise an undefined exception class.

Use v3 for custom APIs

…ime on large jobs, and prevent sending the same request twice when getting details.

Make the API parameter optional, because it causes Diffbot to waste t…

Handle 401 errors from Diffbot.

Faraday::Error::ClientError was renamed to Faraday::ClientError in some later version of Faraday.  Faraday gem needed to be fixed to an older version in the .gemspec file.