input value (in radians)
coversed sine
var v = coversin( 0.0 );
// returns 1.0
var v = coversin( 3.141592653589793/2.0 );
// returns 0.0
var v = coversin( -3.141592653589793/6.0 );
// returns 1.5
var v = coversin( NaN );
// returns NaN
Computes the coversed sine.