Set parameters into the Booster.

        Parameters
        ----------
        params: dict/list/str
           list of key,value pairs, dict of key to value or simply str key
        value: optional
           value of the specified parameter, when params is str key

def set_param(self, params, value=None):
        """Set parameters into the Booster.

        Parameters
        ----------
        params: dict/list/str
           list of key,value pairs, dict of key to value or simply str key
        value: optional
           value of the specified parameter, when params is str key
        """
        if isinstance(params, Mapping):
            params = params.items()
        elif isinstance(params, STRING_TYPES) and value is not None:
            params = [(params, value)]
        for key, val in params:
            _check_call(_LIB.XGBoosterSetParam(self.handle, c_str(key), c_str(str(val))))