System V IPC primitives

Mostly a work in progress to unlock all goodies UNIX provides.

Examples:

import atexit
import sysvipc

sem = sysvipc.semget(sysvipc.IPC_PRIVATE, 1, 0o600)
atexit.register(lambda: sysvipc.semctl(sem, 0, sysvipc.IPC_RMID))

sysvipc.semop(sem, [(0, 1, sysvipc.SEM_UNDO)])

curval = sysvipc.semctl(sem, 0, sysvipc.GETVAL)

sysvipc.semop(sem, [(0, -1, sysvipc.SEM_UNDO)])