added github_events_agent with changes for RAM conserving gem dependencies

this patch contains a github event client , just provide a username or organisation and keep track of your github events 

i havn't made that for any options to track individual repositories, but that could easily be added.
You should include

```ruby
include Oauthable
valid_oauth_providers 'github'
```

and uncomment `gem 'omniauth-github'` in the Gemfile.  Then you can get the user's Github OAuth token from `service.token` and do private things too.