[Feat] Implement `snakepipe socket-play/watch` based on Unix socket

[topheman]

Currently, we can do:

# mirror terminal
cat /dev/null > /tmp/snakepipe.sock && tail -f /tmp/snakepipe.sock|snakepipe render

# master terminal
snakepipe gamestate|tee /tmp/snakepipe.sock|snakepipe render

Those aren't real unix sockets, it's just a simple file tailed. Lets make an implementation with unix sockets.

Proposition:

• Master: snakepipe gamestate|snakepipe socket-play|snakepipe render
• Mirror: snakepipe socket-watch|snakepipe render

Allow overriding the address of the socket (have a default one)

Questions / Constraints

• How to handle when the mirror terminal is started after the main one (which means it misses the header containing the size of level)
  • use bi-directional socket, so that the mirror can request the header when it starts and the master answers
  • master should support multiple mirrors through one socket