Merge branch 'playerspawn-hook' into 'next'

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

src/lua_hooklib.c

@@ -53,6 +53,7 @@ const char *const hookNames[hook_MAX+1] = {
 	"LinedefExecute",
 	"PlayerMsg",
 	"HurtMsg",
+	"PlayerSpawn",
 	NULL
 };