Clean up

Hey @atmos, thanks for this nice gem.

I'm about to build a really simple gem for rails, probably going to call it *warden-github-rails*, which basically adds routing constraint helpers.

It should look something like this:

```ruby
github_auth { resource :user }
github_auth(organization: :github) { resource :admin }
github_auth(team: :sysadmins) { resource :database }
```

Anyways, I came across your gem and started tinkering with it and couldn't really get it to run out of the box. I then started fiddling with the source and made some small changes to make it easier to use with current Bundler standards and newer ruby versions while keeping compatibility with ruby 1.8.

Please, have a look at it. I would appreciate if you integrated the whole thing or parts of it.

I saw that there are API calls through Octokit and others that circumvent Octokit. Any reason for that? If not, I'd work on another pull request to move everything to Octokit, reducing the number of dependencies.

Thanks!