Update change log.
Release 0.0.25.
Meld harness and program into a single cadence.

`lib/proof.t.js` got split into two cadences, with  harness cadence
calling back to a function that would build the program cadence. The
lead to broken error handling, so rather than preserve this pattern, the
two separate cadences have been melded into one cadence so that error
handling for the one cadence handles errors from cleanups, harness and
the program.

Closes #144.
Dedent `lib/proof.js`.

Separate dedent commit so that the previous commit would have a legible
diff.
Merge branch `release-0.0.25` into `master`.
Merge branch `single-cadence` into `master`.