Add WebAssembly test with a little bit macro changes in RayTracer.c.

[wxfred]

In my computer, c version is completed in 31ms, and its webassembly version costs 38ms with -O3 and 43ms with -O1. Expect you to test and update the running time on your computer. By the way, the javascript version needs 140ms (node 14).

ps:

1. Install Emscripten
2. Add emsdk folder to your system env variables
3. Run the build.ps1 on PowerShell
4. Open the output html file on your Chrome