function stdev( a, b ) {
	if (
		a >= b
	) {
		return NaN;
	}
	return SQRT1O12 * ( b-a );
}
Returns the standard deviation of a uniform distribution.

@param {number} a - minimum support
@param {number} b - maximum support
@returns {PositiveNumber} standard deviation

@example
var v = stdev( 0.0, 1.0 );
// returns ~0.289

@example
var v = stdev( 4.0, 12.0 );
// returns ~2.309

@example
var v = stdev( -4.0, 4.0 );
// returns ~2.309

@example
var v = stdev( 1.0, -0.1 );
// returns NaN

@example
var v = stdev( 2.0, NaN );
// returns NaN

@example
var v = stdev( NaN, 2.0 );
// returns NaN