Specify File Encoding on createfile and updatefile #166

Unless I've missed something you cannot specify the encoding of a file when using createfile and update file. This makes it difficult/impossible to properly commit files such as images.

The Gitlab API supports "text" and "base64" for the optional encoding parameter on these calls.
https://github.com/gitlabhq/gitlabhq/blob/master/doc/api/repository_files.md

I would suggest adding a kwarg to these functions which defaults to "text" as it does now by not specifying the encoding when making the call