Problem: logging is not consistent

Solution:

* Remove (kill) zlog class, which turns out to be too hard to use as
  it requires passing class instance all around application.

* Deprecated zclock_log method, which is not an obvious place for a
  default logging method.

* Added zsys_error, zsys_warning, zsys_notice, zsys_info, zsys_debug
  to send log messages to system facility.

* Added zsys_set_logident to define prefix or sender name for searching.

* Added zsys_set_logstream to allow logs to be sent to stdout/stderr.

* Added support for ZSYS_LOGIDENT and ZSYS_LOGSTREAM=stdout/stderr in
  the environment.
Removed temporary debug script