WASM/Emscripten port (SuperTux in the browser)

[Semphriss]

TODO's & FIXME's

Known issues

User experience:

• Crash (Segmentation fault) whenever playing a level
• No audio
  • Now the audio is there, but whenever a sound stop playing, OpenAL crashes (see this issue)
• Extreme lag
• Refreshing makes the game twice as laggy (probably in link with the memory leaks)
• No data is saved when closing the tab/browser or when refreshing
• Add-ons are disabled, but appear as they can't download anything. (If I could compile cURL with OpenSSL for Emscripten...)

Code quality:

• Very poor-quality changes
  • Fix the comments in the CMakeLists.txt file
  • Find a way to not have to put the OpenAL headers from Emscripten in the repo (locate then in the Emscripted SDK)
  • Repair that poor ScreenManager who's probably agonizing at the moment
• Memory leaks in the main function
• Poor memory lifetime management
• HTML template is the default Emscripten template

Potential additions

• Content integration
• Hide the "Quit" button, which doesn't make much sense on the browser (will also be useful for mobile ports)
• A method to save levels to disk and load levels from disk
• A method to save preferences, progress, possibly saved levels and others in the user's browser (localStorage) _{Not cookies please, they have a size limit and they're sent with each request, nor very good for efficiency, privacy and speed}
• A warning before the game launches to tell the users that the web version is laggy and unstable and doesn't save data reliably, and to prefer using the native version instead