Enhancement: upgrade filters to support limit keyword and field filtering.

[jdlrobson]

We have getTaggedTiddlers and the ability to filter tiddlers by a tag e.g. [tag[foo]]

There seems no reason why this shouldn't be extended to custom fields.

Also a limit keyword would be highly useful in akin to the sort keyword. eg. [tag[foo]][limit[2]] would show only 2 tiddlers tagged foo.

Both these would reduce the amount of code in many plugins which do this filtering. TiddlySpace? for instance is frequently looping through tiddlers to find all those with a certain bag field set.

Diff attached.

[MartinBudden]

Fixed in changeset:12472