rake release accepts remote and branches

`rake release` accepts remote(default: `origin`), local branch (default: `master`)
and remote branch(default: `master`)as optional arguments.

    $ rake release[upstream,critical-security-fix,v3]

This will tag and push the commits on your local branch named `critical-security-fix`
to branch named `v3` in remote named `upstream` (if you have commit rights on `upstream`)
and release the gem. This is useful in scenarios where releases keep happening from
older version branches, like in Rails.
Use ENV for rake options
Merge pull request #249 from emilsoman/remote-branch-support

rake release accepts remote and branches