1.4.x

This PR is to address issues #11, #27, #72 and #80 for Riak 1.4.x client. These are fairly small changes to do a little bit of house cleaning on the issues list. I corrected the README by adding a missing 'new' keyword, added the ability to override the returnbody parameter on store, added $this to the return for addIndex to make it consistent with the docblock, and added support for the Riak 204 status code for PUTs.