Proof of concept for a golang implementation of the registry

With this implementation it is possible to host a private registry just by downloading and starting a pre-compiled binary. Should make it much simpler to get started with private registries.

When it comes to pushing layers this implementation should also be much faster (my tests showed 4-5x faster) then the python code, dependent on layer sizes.

For now I only implemented the parts I needed and I have been using that implementation for quite some time now. I would like to make that available for a broader group of people.

The Dockerfile and the README already point to the dotcloud github repository so both will only work after the code is merged. Both parts could be tested by adding calls to checkout e.g. the branch of the pull request though.