Refactor the gem to use onCue's new REST API

This is a rewrite of the gem which uses onCue's new REST API to enqueue jobs. 

#### Additional Changes

1. Change version from 0.9.0 to 1.0.0 (the version of the gem should track the version of onCue's API)

#### Work Remaining

1. Add documentation to methods/classes
2. The `OnCue::Job` class is very simple and should convert the `enqueuedAt` value from the server to a `DateTime` object
3. Write the README file