Fixed the half-done hunger implementation, fixed lots of bugs related to hunger

- Fixed starvation doesn't deal any damage at all (Human->getFood() returns a float, not an int, === 0 won't work so great)
- Added exhaustion for sprinting, walking, jumping and sprint-jumping as per MCPE (these use MCPE values, and yes MCPE does walking exhaustion!)
- Fixed attributes don't get reset after player death
- Added food and hunger regeneration in peaceful difficulty
- Added API methods Living->jump() (motion isn't updated yet, so this won't actually do much if plugins try to use it) and Living->getJumpVelocity()

TODO: implement exhaustion for swimming

src/pocketmine/entity/Attribute.php

@@ -165,6 +165,10 @@ class Attribute{
 		return $this;
 	}
 
+	public function resetToDefault(){
+		$this->setValue($this->getDefaultValue());
+	}
+
 	public function getValue(){
 		return $this->currentValue;
 	}