Lots of boilerplate for now on, will work on upstreaming that in the tool
properly if needed later.
Signed-off-by: Thomas Gazagnaire <thomas@gazagnaire.org>
```
$ fdd init &
$ fdd share /tmp/foo # serve a fresh socketpair on that path
$ fdd test /tmp/foo # read the socketpair and test that it works
```
Instead of `fdd test` (which is only useful for testing), users are expected to
connect to the unix domain socket and call `recvmsg(2)`. They will get one side
of the socketpair. Two different processes can do this and they will be able to
talk to each other.
Signed-off-by: Thomas Gazagnaire <thomas@gazagnaire.org>