Support for connecting via UNIX domain sockets

[runxiyu]

Feature request: Add support for connecting via UNIX domain sockets.

export DATABASE_URL='postgres:///cca-ng?host=/var/run/postgresql'

~/cca-ng/server $ gleam run -m squirrel
   Compiled in 0.23s
    Running squirrel.main
Error: Cannot establish TCP connection

I couldn't connect to the database because I ran into the following
problem while trying to establish a TCP connection to `` at port 5432:
ConnectFailedBoth(Nxdomain, Nxdomain)

Thanks!