Fixed typo
Fixed problem with getTextReference() not always returning a string
Fixed problem with field filter operator not performing string comparisons
Extend the filter mechanism to allow operands to be indirected through a tiddler text reference

In other words, as well as `[sort[myfield]]` to sort by the field
called `myfield`, one can do `[sort{MyTiddler}]` to sort by the field
whose name is in the text of the tiddler `MyTiddler`.
Change the search filter operator to not indirect through a tiddler

Now that we can make any filter operator indirect through a tiddler we
don't need to have that as a special capability of the search operator.
Add the `each` filter operator

This makes it possible to do grouping within lists
Add `eachday` and `sameday` filter operators

These operators will enable us to group the recent changes list by day
Tests for the new filter operators
Group the recent changes list by day