Merge pull request #42 from gamechanger/tl-metadata2

Remove various metadata nonsense which is either completely unused or only used from tests
Merge pull request #43 from gamechanger/tl-worker_id

Stop passing worker_id around all over the f**king place
0.1.0
Merge pull request #44 from gamechanger/tl-unused

Removed various unused imports, assignments and classes
Replaced the record_activity mechanism of indicating aliveness with a heartbeat running on its own thread
Tidied up the implementation of the heartbeat thread
Add a test that repeated heartbeats push out the TTL on the worker activity key
Wrap up starting the heartbeat thread and prevent any race conditions
Remove old activity_timeout construction arg.