Tidy `t/merge/left-singles.t.js`.

See #351.
Tidy `t/merge/left-singles.t.js`.

See #351.
Use `vivify` in `t/merge/left-singles.t.js`.

See #352.
Use `assert` in `t/merge/left-singles.t.js`.

See #351.
Remove `writeInsert`.

See #356.
See #355.
See #107.
See #4.
`writePositions` writes footer separately.

Convert final use of `writePositions` to write footer separately.

See #356.
See #355.
See #107.
See #4.
Remove old `writePositions`.

See #356.
See #355.
See #107.
See #4.
Convert write insert and footer to use streams.

See #356.
See #355.
See #107.
See #4.
Write delete now writes footer separately.

See #356.
See #355.
See #107.
See #4.
`writeBranch` with streams, streams to callbacks.

Implement `writeBranch` using the streaming entry writing functions.

Rework `Transcript` to correctly convert streams errors to callback
errors, I hope, hard to tell if I've managed to capture every possible
error condition.

See #356.
See #355.
See #107.
See #4.
Tidy `t/merge/left-most-unghostable.t.js`.

See #351.
Use `assert` in `left-most-unghostable.t.js`.

See #351.
Use `vivify` in `left-most-unghostable.t.js`.

See #352.
Tidy `t/merge/left-ghost.t.js`.

See #351.
Use `assert` in `t/merge/left-ghost.t.js`.

See #351.
Use `vivify` in `t/merge/left-ghost.t.js`.

See #352.
Fix `vivify` in `t/merge/left-ghost.t.js`.

See #352.
More tidy `empties-non-pivot.t.js`.

See #351.
More tidy `t/merge/branch.t.js`.

See #351.
Tidy `t/merge/race.t.js`.

See #351.