lxd: initial implementation of the daemon

Listens on a unix pipe and optionally tcp, and currently only responds to a
ping command.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
document the ping command

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
lxc: initial implementation of client

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>