docs: def envars_to_markdown(envars, title = "Environment"):
      '''generate a markdown list of a list of environment variable tuples
  
         Parameters
         ==========
         title: A title for the section (defaults to "Environment"
         envars: a list of tuples for the environment, e.g.:
  
              [('TERM', 'xterm-256color'),
               ('SHELL', '/bin/bash'),
               ('USER', 'vanessa'),
               ('LD_LIBRARY_PATH', ':/usr/local/pulse')]
  
      '''
      markdown = ''
      if envars not in [None, '', []]:
          markdown += '\n## %s\n' % title
          for envar in envars:
              markdown += ' - **%s**: %s\n' %(envar[0], envar[1])
      return markdown