function zeros2d( shape ) {
	return filled2d( 0.0, shape );
}
Returns a zero-filled two-dimensional nested array.

@param {NonNegativeIntegerArray} shape - array shape
@returns {ArrayArray} filled array

@example
var out = zeros2d( [ 1, 3 ] );
// returns [ [ 0.0, 0.0, 0.0 ] ]