documentation

Pull request #119: Feature/ZBXNEXT-7065 6.0 D

Merge in WEB/documentation from feature/ZBXNEXT-7065-6.0-D to release/6.0

* commit '8e503018d44b4668abe2d7b76d6679b238077d13':
  plugins.md fixed a typo
  documented PostreSQL by Zabbix agent 2 template changes
  whatsnew603.md better link
  Added to whatsnew603.md
  updated plugins.md
  Added pgsql.queries item to zabbix_agent2.md