new_contents: '''
  Return the version number of the currently installed 'willowtree' package.
  Version numbering follows a major.macro.micro convention, with micro omitted
  if equal to 0.
  
  To display version number in a Python environment, either call:
  
  willowtree.__version__
  
  or, if willowtree is imported as wt:
  
  wt.__version__
  '''
  
  __version__ = '0.9'
  
subject: Add __version__.py to 'willowtree' folder