Import some Lua documentation

I personally find it easier to read the documentation in Emacs
using JavaDoc style comments.

third_party/lua/lstate.c

@@ -275,6 +275,16 @@ static void close_state (lua_State *L) {
 }
 
 
+/**
+ * lua_newthread [-0, +1, m]
+ *
+ * Creates a new thread, pushes it on the stack, and returns a pointer to a
+ * lua_State that represents this new thread. The new thread returned by this
+ * function shares with the original thread its global environment, but has
+ * an independent execution stack.
+ *
+ * Threads are subject to garbage collection, like any Lua object.
+ */
 LUA_API lua_State *lua_newthread (lua_State *L) {
   global_State *g;
   lua_State *L1;