TODO

* [x] improve performance by removing redundancy (service dependencies);
* [x] improve logging and debugging;
* [ ] more testing and compatiblity code for FreeBSD, OpenBSD, NetBSB;
* [+] improve RC compatibility: installability runscript services to /etc/init.d
      (easy to do), and adapt rs semantics to rc (LEVEL/ACTION... quite easy);
  [x] (partly) done with runlevels command support (`sv-stage RUNLEVEL');
* [x] optimize parallel start/stop by using threads/pthread.h (*not easy*);
* [x] improve sv-shutdown compatibilty to SystemV or BSD shutdown/halt utilities;
* [x] set up niceness to daemons;
* [x] add debugging code to runscript (added `SVC_DEBUG' shell function);
* [x] add support to `/etc/sv.conf.local.d' configuration for any service type;
* [x] migrate ./{run,finish} to new `/lib/sv/sh/run' location;
* [x] migrate old (v2) init stage directory from `/etc/sv/.RUNLEVEL'
      to `/etc/sv.init.d/RUNLEVEL';
* [x] log message to syslog(3) (add a new `SV_SYSLOG' and `SV_SYSLOG_INFO' for
      info level message);
* [x] add PID to lock file along with the service command;
* [x] check service lock file before waiting for the lock file;
* [x] check service pidfile for validity before marking a service as started;
* [ ] add the full environment of service to be able to process commands once
      the service is started and removed from service directory;