function log1pexp( x ) {
	return addon( x );
}
Computes the natural logarithm of \\( 1 + \exp(x) \\).

@private
@param {number} x - input value
@returns {number} function value

@example
var v = log1pexp( 1.1 );
// returns ~1.387

@example
var v = log1pexp( 100.0 );
// returns 100.0

@example
var v = log1pexp( NaN );
// returns NaN