function resolve( xdtype, ydtype, policy ) {
	return outputDataType( [ xdtype, ydtype ], policy );
}
Resolves the output ndarray data type for a binary function.

@param {string} xdtype - first input ndarray data type
@param {string} ydtype - second input ndarray data type
@param {string} policy - output ndarray data type policy
@throws {TypeError} third argument must be a recognized data type policy
@throws {Error} must provide data types amenable to type promotion
@returns {string} output ndarray data type

@example
var dt = resolve( 'float64', 'float32', 'complex_floating_point' );
// returns <string>