function meanabs( x, y ) {
	x = abs( x );
	y = abs( y );
	return x + ((y-x)/2.0);
}
Returns the arithmetic mean of `|x|` and `|y|`.

@private
@param {number} x - first number
@param {number} y - second number
@returns {number} arithmetic mean

@example
var z = meanabs( -3.5, -7.5 );
// returns 5.5