Lots of docs updates

core/docs/fields/bag.tid

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+title: $:/docs/fields/bag
+
+The name of the bag from which a tiddler came

core/docs/fields/created.tid

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+title: $:/docs/fields/created
+
+The date a tiddler was created

core/docs/fields/creator.tid

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+title: $:/docs/fields/creator
+
+The name of the person who created a tiddler

core/docs/fields/draftof.tid

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+title: $:/docs/fields/draft.of
+
+For draft tiddlers, contains the title of the tiddler of which this is a draft

core/docs/fields/drafttitle.tid

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+title: $:/docs/fields/draft.title
+
+For draft tiddlers, contains the proposed new title of the tiddler

core/docs/fields/revision.tid

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+title: $:/docs/fields/revision
+
+The revision of the tiddler held at the server