adding arbitrary header fields capability

used by the user attachments upload, and probably a good idea either way.
Style guide enforcing.
Better handling of malformed response bodies.

Without breaking old ways of doing things. Eventually I imagine we want to change the way this wrapper responds entirely.
response objects with status and error hashes like normal objects for example.
version bump.

Outwards api changed, so bumping minor version.
adding upload_file for user resource.
Adding exception for remote resource not found errors.

also raising this error when appropriate.
more sane argument handling.
adding uri to the exceptions.

there's usually good troubleshooting info in the actual uri used, so this will help.
Merge pull request #2 from studentcompetitions/ca-user_file_upload

Ca user file upload