Add extra support for GitHub, Trello and Jenkins

What's inside:

- Upgrade version to 0.2.0
- Upgrade dependencies 
- Improve documentation
- GitHub:
    - Validate requests
    - Assign user
    - Set commit status
- Trello:
    - Validate requests
    - User assigned hook
    - Attach URL to card
- Jenkins:
    - Commit build hook

You might want to change the constructor function to 

`this.config = config || {}`

to get rid of these empty config objects?