Proposal: Replace ephemeral nodes with a unix socket #208

• Remove the send, ping and status subcommands from the receptor command-line. This greatly simplifies the command-line syntax because the only invocation is now node, which can be assumed - so we no longer need subcommand parsing.
• Add parameters --control-socket=<path> and --no-control-socket to receptor. If no options are specified, the control socket defaults to something reasonable like /var/run/receptor.sock.
• Modify the current send, ping and status entrypoints to respond to textual commands sent via the socket file, like echo status > /var/run/receptor.sock.
• Create a new script receptorctl that provides a reasonable command-line syntax for the send, ping and status commands. All it does is validates that the command is sane and then passes it down the pipe, which is either the default or a path specified by --control-socket.

What do people think of this?