beam2/unix: use SOCK_STREAM for beamcat example
beam2/unix: close stream after executing each command in beamcat example
beam2/data: fix bug in Msg.ReadFrom
beam2/unix: simple support for nested streams
beam2/unix: Better debugging messages
beam2: updated example to demonstrate beam as networking layer
beam2/unix: prefix lines with stream ID in example 'beamcat', to make multiplexing more evident
beam2/unix: refactor api to simplify usage and allow native fd passing