documentation

Pull request #1829: feature/ZBXNEXT-8956-7.0-D-API. Enabled communication framework for existing widgets (API).

Merge in WEB/documentation from feature/ZBXNEXT-8956-7.0-D-API to release/7.0

* commit 'e469ed2bdba1780561989831ed02c9670666b347':
  [ZBXNEXT-8956] itemnavigator accepts reference values with ".hostid" (instead of ".hostids")
  [ZBXNEXT-8956] escaping GIT italics
  [ZBXNEXT-8956] updated changelog
  [ZBXNEXT-8956] added "graphid._reference" parameter to widgets capable of listening to graphs data
  [ZBXNEXT-8956] updated parameter requirements
  [ZBXNEXT-8956] clarified second same parameter name
  [ZBXNEXT-8956] unified "Time period" parameter formatting
  updated wording consistency
  [ZBXNEXT-8956] new format idea
  [ZBXNEXT-8956] updated table formatting
  [ZBXNEXT-8956] added "itemid._reference" parameter to widgets capable of listening to items data
  [ZBXNEXT-8956] added "hostids._reference" parameter to widgets capable of listening to hosts data
  updated "Hosts" parameter type
  [ZBXNEXT-8956] updated table formatting
  [ZBXNEXT-8956] added "groupids._reference" parameter to widgets capable of listening to host groups data
  [ZBXNEXT-8956] added "Reference" parameter to widgets capable of broadcasting data
  [ZBXNEXT-8956] refined "Time period" parameter
  [ZBXNEXT-8956] refined "Override host" parameter
  [ZBXNEXT-8956] slightly clarified parameter description
  [ZBXNEXT-8956] enabled communication framework for existing widgets (API)