Add embedded assets, splash screens, and asset loading support

Features added:
- Embedded main.lua and Lua files support (EMBED_MAIN option)
- Embedded assets support (EMBED_ASSETS option)
- Splash screens with dual logo display (always embedded)
- Asset loading progress tracking API (BeginAssetLoading, UpdateAssetLoading, EndAssetLoading)
- Custom font embedding for splash/loading screens
- --log flag for Windows console control
- --no-logo flag to skip splash screens in development
- Python scripts for embedding (embed_lua.py, embed_assets.py, embed_logo.py, embed_font.py)
- Documentation (EMBEDDING.md, ASSET_LOADING.md, SPLASH_SCREENS.md)

This allows building single-executable releases with all Lua code and assets embedded.

include/splash.h

@@ -0,0 +1,6 @@
+#pragma once
+
+void splashInit();
+bool splashUpdate( float delta );
+void splashDraw();
+void splashCleanup();