0.3.0:
  - removed use of yaml in favour of hand parsing the lockfile contents, the
    file as so small it just wasn't worth and i have one core dump when yaml
    failed to parse a (corrupt) file
0.2.0:
  - added an initial polling style attempt to grab lock before entering normal
    sleep/retry loop.  this has really helped performance when lock is under
    heavy contention: i see almost no sleeping done by any of in the interested
    processes
0.1.0:
  - added ability of Lockfile.new to accept a block
0.0.0:
  - initial version