waver : fix font loading and snap build

close ggerganov#19 : add cmake option for single-file wasm build

If enabled, we build ggwave using "-s SINGLE_FILE=1" which causes
the WASM to be embedded inside the .js file.

Otherwise, 2 separate files are produced:
- libggwave.js
- libggwave.wasm

cmake : add install target for waver

waver : install fonts

update .gitignore