v1.3.0

• Allow pex files to be stamped based on their content hash rather than
  the rule hash. This feature is gated behind the content_hashing feaure
  flag which can be abled by adding it to the python.featurefalgs plugin
  config variable (#107)
• Stop pex files starting the bedugger if they're not being ran as part of the
  plz debug command. (#111)