add 'entity.despawn' command

src/logic/CommandsInterpreter.cpp

@@ -373,6 +373,12 @@ public:
             if (!arg->optional) {
                 throw error("missing argument "+util::quote(arg->name));
             } else {
+                if (auto string = std::get_if<std::string>(&arg->def)) {
+                    if ((*string)[0] == '$') {
+                        args->put((*interpreter)[string->substr(1)]);
+                        continue;
+                    }
+                }
                 args->put(arg->def);
             }
         }

src/logic/PlayerController.cpp

@@ -241,6 +241,7 @@ void PlayerController::update(float delta, bool input, bool pause) {
     if (!pause) {
         if (input) {
             updateKeyboard();
+            player->updateSelectedEntity();
         } else {
             resetKeyboard();
         }

src/logic/scripting/lua/libplayer.cpp

@@ -140,8 +140,8 @@ static int l_get_selected_block(lua::State* L) {
 
 static int l_get_selected_entity(lua::State* L) {
     if (auto player = get_player(L, 1)) {
-        if (player->selection.entity) {
-            return lua::pushinteger(L, player->selection.entity);
+        if (auto eid = player->getSelectedEntity()) {
+            return lua::pushinteger(L, eid);
         }
     }
     return 0;