Refactor: introduce telinit and a new initctl tool w/ API

- Reduce size of `helpers.c`, for linking against new `initctl` tool,
  by moving out functions to `pid.c` and `exec.c`
- Add `AF_UNIX` API to Finit, to complement old `/dev/initctl` FIFO
- Let old FIFO API be used by init/telinit: `init <q | 1-9>`
- Move all advanced initctl code from `client.c` to `initctl.c`, yes
  its a bit confusing to call the *new* tool the same as the old FIFO
  but this is more in line with what, e.g Upstart does.
- Move all advanced server side code from `plugins/initctl.c` to `api.c`
- Update TODO with upcoming inetd syntax change and dynamic events.
- Temporarily fix display of inetd services from `initctl status -v`

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

private.h

@@ -30,6 +30,7 @@
 
 uev_ctx_t *ctx;			/* Main loop context */
 
+int       api_init         (uev_ctx_t *ctx);
 int       client           (int argc, char *argv[]);
 
 void      service_bootstrap(void);