Add some player lua methods

Adds u.clear_inventory() and u.giveobj(new.obj("rock")) and some other minor stuff.

include/extern.h

@@ -1676,6 +1676,7 @@ E int FDECL(l_selection_register, (lua_State *));
 /* ### nhlobj.c ### */
 #if !defined(CROSSCOMPILE) || defined(CROSSCOMPILE_TARGET)
 E void FDECL(nhl_push_obj, (lua_State *, struct obj *));
+E int FDECL(nhl_obj_u_giveobj, (lua_State *));
 E int FDECL(l_obj_register, (lua_State *));
 #endif