Now both the insertafter and insertbefore filter operators have similar
wording in their documentation tiddlers, making it more clear that the
"start" and "end" suffixes are only available in the two-parameter form.
* Implement insertafter operator (like insertbefore)
Currently, the behavior of insertafter if the target is not found is to
append the inserted tiddler to the end of the list, like insertbefore
does. In the next commit, we'll add a suffix to customize what both
insertafter and insertbefore do when the target is not found.
* Add failing tests for insertafter suffixes
Also includes tests for insertbefore suffixes (start/end), since we'll
be implementing both of those at the same time.
* Add start/end suffixes for insertafter/before
The tests that exercise the start/end suffixes now pass.
