Feature emit events from mocks

PR for https://github.com/Runnable/docker-mock/issues/12

Events can be sent like this:

```javascript
  var dockerMock = require('docker-mock');
  dockerMock.listen(5354);
  dockerMock.events.stream.emit('data', JSON.stringify({status: 'die', from: '..', id: '...', time: '...'}));
  // or
  dockerMock.events.stream.emit('data', dockerMock.events.generateEvent());

```