code: def prepare(doc):
      
      doc.mustache_files = doc.get_metadata('mustache')
      if isinstance(doc.mustache_files, basestring):  # process single YAML value stored as string
          if not doc.mustache_files:
              doc.mustache_files = None  # switch empty string back to None
          else:
              doc.mustache_files = [ doc.mustache_files ]  # put non-empty string in list
      # with open('debug.txt', 'a') as the_file:
      #     the_file.write(str(doc.mustache_files))
      #     the_file.write('\n')
      if doc.mustache_files is not None:
          doc.mustache_hashes = [yaml.load(open(file, 'r').read()) for file in doc.mustache_files]
          doc.mhash = { k: v for mdict in doc.mustache_hashes for k, v in mdict.items() }  # combine list of dicts into a single dict
          doc.mrenderer = pystache.Renderer(escape=lambda u: u, missing_tags='strict')
      else:
          doc.mhash = None
docs: Parse metadata to obtain list of mustache templates,
          then load those templates.