Add reshape function

[coreylowman]

This would only work for two tensors with the same number of elements. This can be used for #34

[coreylowman]

First working version in 1215ed5. Note that this requires nightly because a type Flat = [(); M * T::NUM_ELEMENTS] was added for arrays that allows you to check that two arrays have the same ::Flat.

[coreylowman]

Another approach that is slightly more readable and self contained (but still requires #![feature(generic_const_exprs)]):

struct True;

trait ConstAssert {
    type Result;
}

struct ConstEq<const A: usize, const B: usize>;

impl<const A: usize> ConstAssert for ConstEq<A, A> {
    type Result = True;
}

fn copy<Lhs: Count, Rhs: Count>(lhs: &Lhs, rhs: &mut Rhs)
where
    ConstEq<{ Lhs::NUM_ELEMENTS }, { Rhs::NUM_ELEMENTS }>: ConstAssert<Result = True>,
{
    let l = lhs.ref_first() as *const f32;
    let r = rhs.mut_first() as *mut f32;
    unsafe {
        std::ptr::copy_nonoverlapping(l, r, Lhs::NUM_ELEMENTS);
    }
}