Prepare a 0.3.1 release.
Merge pull request #54 from apenney/031-release

Prepare a 0.3.1 release.
Use fully qualified volume paths
Implement 'instances' method for all LVM resources

This method makes it possible to use constructs like:
  resources { 'physical_volume': purge => true, noop => true, }
  resources { 'logical_volume':  purge => true, noop => true, }
  resources { 'volume_group':    purge => true, noop => true, }
Set default LV unit size to MB