(she helped port important drawing code!)

(I might've missed some, though)

These functions were already here before, and I /swear/ the slope
physics became slightly less glitchy after switching to them...
Only issue is the slope plane mapping code hasn't been properly
converted yet, so they don't render properly for now.

m_vector removal to come later. The little thing commented out in it
is so I could revert the weird tables.c change.

This is incredibly messy and probably needs redone differently at
some point, but... fuck it.