Replace most To* traits by Into

[tomaka]

See #214

[kvark]

I'm good with it. Calling for @cmr @bjz @csherratt to look as well.

[ghost]

I don't have any large objections, just one question is there a way to do this without the the extra assignment?

// maybe?
angle.into::<Deg<_>>(); 

Just don't want to break the ability to write one liners.

[tomaka]

I think you can write <Deg<_> as From<_>>::from(angle), and type ascription will eventually make it cleaner by making it possible to write angle.into():Deg<_>.into():Rad<_> for example.

But the major idea is that for example functions that take a Rad<S> should take a T where T: Into<Rad<S>> instead, so that they can handle both degrees and radians.

For example if we add impl<S, T> Add<T> for Vector3<S> where T: Into<Vector3<S>> { ... }, then we'll be able to write: let v = Vector3::new(0.0, 0.0, 0.0); v + (1.0, 0.0, 0.0);

[ghost]

Freaken awesome tomaka!

So Vector4::new(...) * 2.0 could exist.

[tomaka]

In fact you can just write Deg::from(angle) and it should work.

[kvark]

I guess @csherratt is good with the change. Merging now.
Thanks @tomaka !

[tomaka]

Next version to be published should have its minor version bumped!
But I'll make two or three other changes before.

[FredrikNoren]

Looks like this never made it into the docs (docs still refer to ToMatrix4 etc.)

Awesome lib btw! Looks very well written