* add new 'envchk'function to check adblock environment only,
  i.e. check volatile firewall rules or uhttpd instances
  without list updates
* add new optional parm 'adb_loglevel',
  set it to "0" to mute output (print only errors)
* set hotplug priority to '90' as well (missed in the last commit)
* documentation update
* cosmetics

Signed-off-by: Dirk Brenken <dev@brenken.org>