Added support for relative dates.
- Thanks to QWp6t (#3) for the suggestion and initiative!
  When calling the `getLifestream()` method, a new array key was created
  named `date_relative` which holds the relative date between the action
  and the current date.
- Added support for multiple language parameters
- Added time transalation strings into the language classes
- Added language tests, Updated the consistency tests
Rewrote the Github provider
- I was not very happy with the Github provider, it was too buggy with
  some creation and push events. So I rewrote it and added support for
  other event types.