Optionally use $PULSE_SERVER to find pulse socket

[mattimo]

The normal libpulse uses this environment variable to determine which socket to connect to. It might make sense to do the same. (see: https://github.com/pulseaudio/pulseaudio/blob/master/src/pulse/client-conf.c#L51)

Alternatively the socket path could be made configurable so that users who really need it can do a more complicated dance to figure out what environment variables to use in order to find the native socket.

Either way is fine for me, and I could just open an PR depending on preference.

[mattimo]

Ok, stupid me. I should open my eyes better when reading the documentation. Sorry about the noise, I'll get another coffee right away.