Merge pull request #15 from caring/master

Test on modern rubies
Method so we can add Faraday middleware.
Allow saveable attributes to be referenced on a new object.

Allows use in forms, otherwise you need to initialize with a set of attributes.
Also we shouldn’t append :id each time we call `savable_attributes`
Fix dependencies so builds are consistent.
Lock to webmock 1.18.0 for testing.
Show more features in the README example.
Merge branch 'attr-saveable-bug' into caring_master