Add --remove-uncalled-funcs

[BobVarioa]

Fixes most of #85. Not enabled by default but is a relatively safe optimization. It might break some indirects? (if they don't use funcRef somehow)

Example:

$ ./porf -e "console.log(1)" -b --no-run
wasm size: 39234 bytes
$ ./porf -e "console.log(1)" -b --no-run --remove-uncalled-funcs
wasm size: 27428 bytes
$ ./porf -e "console.log(1)" -b --no-run --remove-uncalled-funcs --uncalled-funcs-runs=5
wasm size: 22441 bytes

Some other examples for comparision:

$ ./porf -e "Porffor.miniLog(1)" -b --no-run 
wasm size: 23326 bytes
$ ./porf -e "Porffor.miniLog(1)" -b --no-run --remove-uncalled-funcs
wasm size: 15604 bytes
$ ./porf -e "Porffor.miniLog(1)" -b --no-run --remove-uncalled-funcs --uncalled-funcs-runs=5
wasm size: 11970 bytes
$ # and our obvious winner:
$ ./porf -e "Porffor.numberLog(1)" -b --no-run
wasm size: 115 bytes

A 30% wasm size reduction for console.log 🎉 (and potentially up to 42% 👀)

[CanadaHonk]

WIP/partial review as doing some internal changes which will affect this soon(tm)