Gild the shortest edit merge algorithm
Back out OT merge. Causes bugs downstream.
Add concat operator
Add enumerate spec
Update checklist
0.2.5
Revert "Back out OT merge. Causes bugs downstream."

Turns out, merging worked just fine.

This reverts commit 3362565123214afe161f27470ca185e11b3196c8.
Fix regression in filter output

In a filter block observer, we cannot short circuit a range change just
because the predicates did not change.  The predicates can be the same
even when the underlying content *does*, in which case we certainly do
need to propagate a range change to the output.  But we still want
to short circuit if the output would not have been changed by the swap.

This patch fixes the regression while also preventing flickering.
0.2.6