Merge pull request #4 from brb/feature/update-lock

Update lock_db values
Add wait_for_release/2 which notifies a caller when a lock is released

Add unit test for wait_for_release/2
Add exports for lock/4 and release/3 to enable access to their versions
exposing the timeout parameter

Change some formatting to remove excessive newlines and refactor the
notification to callers into two internal notify_lock_waiter and
notify_release_waiter functions

Update README to reflect changes