Add modules for Releases API

This PR is dependent on:
* https://github.com/edgurgel/tentacat/pull/5
* https://github.com/edgurgel/httpoison/pull/1

This will add two modules; one for manipulating releases and another for manipulating release assets.

Unfortunately Erlang's SSL does not currently support SNI at the time of writing. This is required for interacting with the upload endpoint. The code has been written and should work, but it is commented out for now. R17 will support SNI and can be seen [in this commit](https://github.com/erlang/otp/commit/bc8b6bf58c96f8d5a07146ddea145f71fe8c8956) on the OTP project.

I can rebase and cleanup the history if necessary since this is a branch of a branch PR.

You can see a complete working copy of all this before merging by cloning the 'fork' branch of my tentacat repository. It pulls in the HTTPoison forked dependency.