Minor changes & simplifications to Lua interface. 5 new functions.

This changes all typical vector interpolation functions that get
value, time, loopType, pingPong, ease as args from the Lua state;
use unified functions for all value type occurances.
This fixes the slightly annoying problem that it was not possible to
pass a boolean true to pingPong or ease, because lua_tonumber() would
always return 0 in that case.

Also changed:
- obj_getWorldPosition() now takes optional x,y-vector

New:
- obj_getWorldPositionAndRotation() is a more efficient shortcut,
	as often both position and rotation are retrieved together,
	and the underlying matrix chain operation is rather expensive.
- entity_getEmitter()
- entity_getNumEmitters()
- setSceneColor2()
- getSceneColor2()

BBGE/RenderObject.h

@@ -206,6 +206,7 @@ public:
 
 	Vector getAbsoluteRotation();
 	float getWorldRotation();
+	Vector getWorldPositionAndRotation(); // more efficient shortcut, returns rotation in vector z component
 	Vector getNormal();
 	Vector getForward();
 	void setOverrideCullRadius(float ovr);