Convert some methods to trait methods

[timschmidt]

Via Andrei:

Take for example, this:

    /// Returns a new CSG translated by x, y, and z.
    ///
    pub fn translate(&self, x: Real, y: Real, z: Real) -> CSG<S> {
        self.translate_vector(Vector3::new(x, y, z))
    }
    
    /// Returns a new CSG translated by vector.
    ///
    pub fn translate_vector(&self, vector: Vector3<Real>) -> CSG<S> {
        let translation = Translation3::from(vector);
        
        // Convert to a Matrix4
        let mat4 = translation.to_homogeneous();
        self.transform(&mat4)
    }

Rust does not have function overloading, but what could be done in this case, is something like:

    pub fn translate(&self, vector: impl Into<Vector>) -> Self {
        let translation = Translation::from(vector);
        let mat = translation.to_homogenous();
        self.transform(&mat);
    }

If this method is on a trait, and the trait bounds are correct, then as long as CSG2D & CSG3D implement the transform(&self, ...) -> Self, they get translate for free, as the default trait method.
On top of that, Into<Vector> can be implemented for all kinds of stuff, so you could do a.transform((1, 2, 3)), a.transform([1.0, 2.0, 3.0]) if you'd like with just one method.

[TimTheBig]

IO would also be nice so other crates could be used as extensions

[timschmidt]

Some progress made on this in the multimodal branch