Load completion list for ROBOFORTH commands.

def load_forth_commands(self, help_dir):
        ''' Load completion list for ROBOFORTH commands. '''
        try:
            help_file_path = os.path.join(help_dir, 'roboforth.txt')
            commands, help_text = self.parse_help_text(help_file_path)
        except IOError:
            print(self.style.warn('Warning: ',
                                  'Failed to load ROBOFORTH help.'))
            return
        self.commands['forth'] = commands
        self.help['forth'] = '\n'.join([self.style.theme('Forth Commands'),
                                        help_text])