Add an analytic ray-capsule intersection test

[joonazan]

I need ray-capsule intersections and was surprised that they were really slow because they are implemented via GJK, so I wrote an analytical version.

I did not solve the equations myself. I adapted Inigo Quilez's GLSL. The result is more optimized than anything else I can find.

On my machine the analytical version takes about 5 ns per query hit or miss. GJK takes 50 ns on a miss and 400 - 700 ns on a hit.

The analytical version's error is smaller, too. Could be better, though. In extreme corner cases errors of 1e-3 can be observed at scales of a few units using f32.

[joonazan]

Replaced the initial AI version of the collision check with a handwritten one that is shorter and is much more numerically stable due to cross products instead of dot products followed by a * b - c * d. Worst case error didn't improve much but it is way better on average.