read config from config_dir
        if config_dir is None, clear to default config
        clear will clear to default before reading new file

def read(self, config_dir=None, config_name=None, clear=False):
        """
        read config from config_dir
        if config_dir is None, clear to default config
        clear will clear to default before reading new file
        """

# TODO should probably allow config_dir to be a list as well
        # get name of config directory
        if not config_dir:
            config_dir = self._defaults.get('config_dir', None)
        if not config_dir:
            raise KeyError('config_dir not set')

        # get name of config file
        if not config_name:
            config_name = self._defaults.get('config_name', None)
        if not config_name:
            raise KeyError('config_name not set')

        conf_path = os.path.expanduser(config_dir)
        if not os.path.exists(conf_path):
            raise IOError("config dir not found at %s" % (conf_path,))

        config = munge.load_datafile(config_name, conf_path, default=None)

        if not config:
            raise IOError("config file not found in %s" % (conf_path,))

        if clear:
            self.clear()

        munge.util.recursive_update(self.data, config)
        self._meta_config_dir = conf_path
        return self