Release Name: 0.6.1

Notes:
* Added working implementations for Process.uid, Process.getpriority and Process.setpriority


Changes:
* Added the Process.uid method. This method returns a user id (really, the RID
  of the SID) by default, but can also take an optional parameter to return
  a binary SID instead at the user's discretion.
* Added working implementations of Process.getpriority and Process.setpriority.
  Note they they only work for processes, not process groups or users.
* Set license to Artistic 2.0, and updated the gemspec.