update physics only if not already done

added sound when player runs out of stamina
added timeout, unlocked on total regen
stamina regen divided by 2 if player walk
added new icon stamina
added from "playerplus" cactus hurts

Add compatibility to HUD bars mod.

Cleanup and rearrange code. Add SPRINT_STAMINA variable for limiting sprinting, Update README, change default value of SPRINT_TIMEOUT to 0.5.