Add PlayerSpawn hook to Lua
I don't know how I did this but I did. Something about staring at code from 3AM till 5AM...
Here's a test script too:
```Lua
addHook("PlayerSpawn", function(player) player.health = 99 end)
```
See merge request !48
That's supposed to be run once a frame, not once per hook
per mobj per frame you moron. If you just run it seven
thousand times a frame, of course your framerate will drop.
Dummy, what do you think you're doing? If you
just push mobjs and players into Lua all willy-
nilly everywhere, you'll wind up generating
tons of metatables and stuff you arne't even
gonna use!
Oh. Thanks me, I'm really smart.
This _should_ solve some significant performance
issues Lua experiences. If not, I will be very
upset for having wasted so much time and effort.
There will be bugs, this kind of thing needs to
be thuroughly tested and this is just the first
iteration of it.
