Improved API coverage, better test coverage.

This release introduces much improved API coverage, along with options on many of the endpoints and improved test coverage.

• Ability to star and unstar an entry, or an array of entry IDs.
• Ability to retrieve subscriptions created after specified date.
• Ability to pass parameters to the entries endpoint.
• Ability to unsubscribe from a subscription.
• Ability to retrieve a feed.

The gem now supports the majority of the Feedbin API, minus tagging.

Now, I'm going to shut up and 🚢 it.