function median( p ) {
	return addon( p );
}
Returns the median of a Bernoulli distribution.

@private
@param {Probability} p - success probability
@returns {PositiveNumber} median

@example
var v = median( 0.1 );
// returns 0.0

@example
var v = median( 0.8 );
// returns 1.0

@example
var v = median( 1.1 );
// returns NaN

@example
var v = median( NaN );
// returns NaN