Documentation for format filter operator (#4895)

* Documentation for format operator

* Examples for format operator

editions/tw5.com/tiddlers/filters/examples/format Operator (Examples).tid

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+created: 20201020102735123
+modified: 20201020104004306
+tags: [[Operator Examples]] [[format Operator]]
+title: format Operator (Examples)
+type: text/vnd.tiddlywiki
+
+These examples use the tiddler HelloThere.
+
+Created date with no format string specified:
+<<.operator-example 1 "[[HelloThere]get[created]format:date[]]">>
+
+Created date with a format string supplied as operator parameter:
+<<.operator-example 2 "[[HelloThere]get[created]format:date[DDth MMM YYYY]]">>
+
+Modified date shown as a relative date:
+<<.operator-example 3 "[[HelloThere]get[modified]format:relativedate[]]">>

editions/tw5.com/tiddlers/filters/format.tid

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+caption: format
+created: 20201020100834443
+modified: 20201020104004271
+op-input: a [[selection of titles|Title Selection]]
+op-output: input strings formatted according to the specified suffix <<.place B>>
+op-parameter: optional format string for the formats
+op-parameter-name: C
+op-purpose: format the input string according to one of supported formats
+op-suffix: one of supported formats
+op-suffix-name: B
+tags: [[Filter Operators]] [[String Operators]]
+title: format Operator
+type: text/vnd.tiddlywiki
+
+<<.from-version "5.1.23">>
+
+The suffix <<.place B>> is one of the following supported string formats:
+
+|!Format |!Description |
+|^`date` |The input string is interpreted as a UTC date and displayed according to the DateFormat specified in the optional operator parameter. (Defaults to "YYYY MM DD 0hh:0mm") |
+|^`relativedate` |The input string is interpreted as a UTC date and displayed as the interval from the present instant. Any operator parameters are ignored. |
+
+<<.operator-examples "format">>