Default com_maxfps to 0 under Emscripten. Under Emscripten the browser
handles throttling the frame rate. Manual framerate throttling interacts
poorly with Emscripten's browser-driven event loop.
This enables several things:
* Optionally load pk3 files from a web server at runtime instead of bundling them with Emscripten at build time
* Set command line arguments via URL param
* It's not ugly