documentation

Pull request #1234: feature/ZBXNEXT-743-7.0-D: New widget: Gauge.

Merge in WEB/documentation from feature/ZBXNEXT-743-7.0-D to release/7.0

* commit '4605ca4c7ec7bf8e6179291ea6d8c243edffd8fc':
  [ZBXNEXT-743] Added double quotes to suffixes examples
  [ZBXNEXT-743] Gauge widget also supports memory suffixes
  [ZBXNEXT-743] Fixed mistakes; added info on suffixes support
  [ZBXNEXT-743] Added image of widget styles; removed unused image
  [ZBXNEXT-743] Updated gauge images; updated formatting
  [ZBXNEXT-743] Updated macros supported in the description of the *Item value* and *Gauge* widget
  [ZBXNEXT-743] New widget: Gauge