Fix enabling extension in Getting Started guide.
Fix Worker Handler address in Create Worker guide.

The Worker Handler runs on port 61003 by default. The Client Handler
runs on port 61002, which would break the example.

Signed-off-by: Jacob Kiers <jacob@alphacomm.nl>
Add installation instructions for Ubuntu 14.04.

Signed-off-by: Jacob Kiers <jacob@alphacomm.nl>
Merge pull request #38 from jacobkiers/fix-getting-started

Fix enabling extension in Getting Started guide.
Avoid call_user_func, by passing `$this`.
Fixed php-cs-fixer bc-break: ALL_LEVEL to SYMFONY_LEVEL.
Force MessageInterface for onWorkerHandlerMessage.
Refactored heartbeats within WorkerCommunication.

- Removed undefined constant STATUS_OK. (unreachable code).
- Extracted handleHeartbeatResponse.
- Grouped handling of READY, RESULT and REGISTER.
CS Fix: casting requires space.
Added missing php docs.