Refactor the project to use namespaces.

Pull request to track the status of the namespace update. If you wish to take on any of these tasks, please email me at dan@block8.co.uk.

### Core
- [ ] Auth classes
- [ ] Cache classes
- [ ] Service classes
- [ ] URI Template Parser ( Can this be pulled in via composer? )
- [ ] I/O classes
- [ ] Service classes
- [ ] API client

### Tests
- [ ] Set up in Travis
- [ ] Update tests

### Examples
- [ ] Update examples to use new structure