docs: def load_credentials_from_file(username):
      '''Loads password for `username` from a file.
  
      The file must be called ``.tm_pass`` and stored in
      the home directory. It must provide a YAML mapping where
      keys are usernames and values the corresponding passwords.
  
      Parameters
      ----------
      username: str
          name of the TissueMAPS user
  
      Returns
      -------
      str
          password for the given user
  
      Raises
      ------
      OSError
          when the file does not exist
      SyntaxError
          when the file content cannot be parsed
      KeyError
          when the file does not contains a password for `username`
  
      Warning
      -------
      This is not safe! Passwords are stored in plain text.
      '''
      filename = os.path.expandvars(os.path.join('$HOME', '.tm_pass'))
      try:
          with open(filename) as f:
              credentials = yaml.load(f.read())
      except OSError as err:
          raise OSError(
              'No credentials file:\n{0}'.format(filename)
          )
      except Exception as err:
          raise SyntaxError(
              'Could not be read credentials from file:\n{0}'.format(str(err))
          )
      if username not in credentials:
          raise KeyError(
              'No credentials provided for user "{0}"'.format(username)
          )
      return credentials[username]