Be a little smarter about logging requests and responses.
Convert MBRequest to ARC.
Convert more code to ARC.
Add the status code to the error user info dictionary.
Remove unnecessary synthesize statements.
Update README for ARC and JSON.
Try to parse the responseJSON even if there was an error.

This allows users to access the JSON object even if the server returns
a status code not in the 200-299 range.
Remove MBJSON and add JSONReadingOptions property.
Remove README section about MBCommon localization.