Prepare for Initial Stable 1.0 release

This PR is for discussion around the work towards a stable 1.x release.

This release will still implement a **JSON-RPC 2.0** client for the **Guzzle 3.x** project. For discussion around implementing a client for Guzzle 4.x, please see the [relevant issue](https://github.com/graze/guzzle-jsonrpc/issues/10).