Transforms env-strings to python.

def _val_from_env(self, env, attr):
        """Transforms env-strings to python."""
        val = os.environ[env]
        if attr in ('rules', 'exclude_rules'):
            return self._rules_from_env(val)
        elif attr == 'priority':
            return dict(self._priority_from_env(val))
        elif attr in ('wait_command', 'history_limit', 'wait_slow_command',
                      'num_close_matches'):
            return int(val)
        elif attr in ('require_confirmation', 'no_colors', 'debug',
                      'alter_history', 'instant_mode'):
            return val.lower() == 'true'
        elif attr == 'slow_commands':
            return val.split(':')
        else:
            return val