Movement Tweaks - Fixes Coffee, Hyperzine, VTEC, shoes, etc

Created by: cloroxygen

This allows negative tally sums in human_movement.dm to speed the user up.

As it stands speed is capped by several factors, as such hyperzine cannot increase the speed of a normal player in jumpsuit and shoes.

I think this also balances the slowdown variable. It may ultimately need tweaking as normal speed is subjective but this is a step in the right direction.

Another caveat: I was only able to test this locally where latency isn't an issue, regardless, going from my modifications it should pose no problem to adjust things to the established development group's current palate.

This is all interrelated to #9560, however it may not address all issues brought forth.