Add trigonometry functions

[gauteh]

It would be useful to have trignometric functions available through some trait. Ideally I would wish for generic functions implementing sin, cos, etc. So that they can be used not as a member function, but as a standalone generic function (which in my subjective opinion improves the readability of rust implemented math):

fn sin<T: FloatTrig>(arg: T) -> T { T.sin() }

Is there some other standard crate already doing this? There has probably been discussions related to this on the rust stdlib.

Mentioned in by @tuxmark5 in #178 (comment)_

[gauteh]

Nevermind.. I don't know why I didn't see those in the docs in the first place.