Add rampbugfix to CKZ

[zer0k-z]

Addresses #62.
In CS2, rampbug happens when there's a slope that gets in our way. It's tiny, and will send you way off the ramp once you collide with it.
The solution is to keep track of the previous valid plane, then we move the trace along the previous normal (or in 26 different directions if this normal fails) to see if we can dodge this mini ramp.

If we happen to hit a plane, check if it's a plane that will potentially knock you away still. If it's not a valid plane, we keep moving away from the original plane.

If we moved really far yet we still couldn't dodge it, that means the ramp is sufficiently big and is most likely a legitimate ramp. In that case, we don't do anything.

And if we don't hit anything, trace back to the original end point. Some scenarios can happen:

1. The most common case is that the parallel trace will hit a legitimate ramp. We make sure the trace is valid, move the player there, and clip the velocity according to the normal that we just got.
2. It's possible that the parallel trace hits nothing. Then we can just move the player straight to the original end spot, no velocity clipping needed.
3. In very unlikely cases, the parallel trace will not hit anything, but tracing back to the original end will make the trace hit the invalid plane again. The current fix doesn't do anything about this yet, but in theory we could just extend the original end (and therefore the parallel traces) to get out of this situation and either end back up in 1 and 2 again.