Test Go version 1.3 in TravisCI

Also remove 1.1, compilation time is much longer
than for others.
Add support for Token source and Addon register Urls
Add interfaces for Api and Token
Update README
Use Request data as []byte instead of url.Values
Add RegisterAddon method

This also allows to send data in json format,
not only as url encoded content.
Version 0.3.0

* Introduce custom cloudControl structure types
* Add possibility to create custom API instances
* Add custom Token source URL
* Add custom Add-on register URL and RegisterAddon methods
* Create Api and Token interfaces, so Requests uses them
* Request data is now also accepted as JSON
* Improve documentation
* Fix of bugs