Implement marking tasks as done and test
Update embedded coordinator interface implementation
Add Done method to etcd coordinator and fix taskmgr tests
Add test for marking tasks as done
Remove debugging log line
Test at different concurrency levels
Use multiple chans for task state transitions
Merge branch 'master' into 52-delete-done-tasks
Simplify task releasing and fix timing sensitive embedded test
Merge pull request #58 from lytics/52-delete-done-tasks

Add task completion support