Support more trigonometric functions

[PaddiM8]

It seems like arc functions and hyperbolic functions are lacking, which is a bit limiting. Having these would make it almost as feature-rich as f64.

[schungx]

Since none of the trig functions necessarily maintain precision (or have perfect precision in the first place), it really might actually be better to first convert the Decimal to f64, do whatever trig function, then convert the result back.

Instead of giving a false impression to users that, somehow, Decimal trig functions are more precise than f64 ones (they are not).