Multi-process instead of multi-threaded

[libv]

Use SHM for shared kms fd and shared data.

The current design is threaded, so we cannot easily restart things. By making it multi-process, we can send signals to individual processes.

Depends on issue #10

[libv]

SHM is not a solution. While mutex can be made robust (so they can catch process dying), this is no true for pthread_cond, even though the latter can be set to "shared", which makes one assume that sharing these sensibly across processes is a good thing to do.

Giving up on SHM, moving to sockets. 2.5manweeks burned.