Adds the releases api

NOTE: [Upload release asset](https://developer.github.com/v3/repos/releases/#upload-a-release-asset) is not implemented.

It's unclear how you'd like this implemented. It uses a different URL which means some how
the hosts address needs to change for this upload. It also has to send a potentially large
file meaning the file should probably be streamed, rather than passing the entire binary
blob to the function call.
@greggman I'm wondering where this unknown symbol comes from, I think it should be a simple apostrophe...