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()
More new Lua functions.

- shot_getMaxSpeed()
- shot_setMaxSpeed()
- shot_getHomingness()
- shot_setHomingness()
- shot_getLifeTime()
- shot_setLifeTime()
- getScreenVirtualSize()
Make some ints floats.