function mode( a, b ) {
	return addon( a, b );
}
Returns the mode of an arcsine distribution with minimum support `a` and maximum support `b`.

@private
@param {number} a - minimum support
@param {number} b - maximum support
@returns {number} mode

@example
var y = mode( 0.0, 1.0 );
// returns 0.0

@example
var y = mode( 4.0, 12.0 );
// returns 4.0

@example
var y = mode( -4.0, 4.0 );
// returns -4.0

@example
var y = mode( +Infinity, 4.0 );
// returns NaN

@example
var y = mode( -Infinity, 4.0 );
// returns -Infinity

@example
var y = mode( 1.0, NaN );
// returns NaN

@example
var y = mode( NaN, 2.0 );
// returns NaN