Change subprocess call to wasm call

[zhaxzhax]

why

Since p2p-chat is a interface using to call a subprocess p2p-net, this logic can not be multiplexing in web, Android. As we all know, wasm has higher compatibility than the bin program.
Luckily ( fixed wasi support (I think) #97 ), net2-rs seems like add the support of wasm. So it looks like rust-libp2p will have the support of wasm also.
I would like a try to change the bin logic into wasm.