sundry tweaks

- prevent infinite loop and warn when a game has no card fields
- choice fields are no longer ignored if they have no choices defined
- templates can now have the same name as their game folder (no hyphen needed)
- indent made by 4 spaces is now considered a tab (but will still produce a warning let's no kid ourselves)

src/data/game.cpp

@@ -66,7 +66,11 @@ IMPLEMENT_REFLECTION(Game) {
   REFLECT_NO_SCRIPT(auto_replaces);
 }
 
-void Game::validate(Version v) {
+void Game::validate(Version v) {
+  // check that we have at least one card field
+  if (card_fields.size() < 1) {
+    throw Error(_ERROR_1_("no card fields", name()));
+  }
   Packaged::validate(v);
   // automatic statistics dimensions
   {