v2.2.1: Merge pull request #20 from denpaforks/master

Check that lock file exists, before trying to delete it.

v2.1.0: Merge pull request #12 from texthtml/feature/factory-interface

add \TH\Lock\Factory interface

v2.0.0: Merge pull request #10 from mathroc/feature/cleanup-identifier

remove $identifier from LockFile