Merge remote-tracking branch 'origin/merge-nameserver-server'

* origin/merge-nameserver-server:
  evsched: updated comments and renamed some attributes
  evsched: add missing header
  evsched: removed deprecated evqueue and streamlined the API
  remove void comments
  minor formating fixes
  utils: renamed knot_serial_compare and added headers
  zone: common API for controlling zone timers
  nameserver: Merged nameserver_t -> server_t
  nameserver: removed redundant attributes