Client implementation using Guzzle's Http module and Oauth plugin.

This is probably going to become the default.
API for multiple simultaneous uploads.

Actually implemented for Guzzle client (cba to do the others as I plan to deprecate them.)
Factored out common parts of packManipulator.
Added multi-upload to pack manipulator example.
Merge pull request #23 from JonathanO/multi-upload

Multi upload