Remove a superfluous variable from `readLeaf`.

Removed a superfluous `path` variable from `readLeaf`.
Remove `length` property from `page`.

Removed the `length` property from the `page` object. This was a
property cached as meta data so that the balancer could reference it as
meta data, should the cache entry's actual data get purged.

See #63.
Store meta data in balancer data structures.

The balancer now caches the meta data it needs into the linked list
structure it uses to plan splits and merges.

Closes #63.

There is no longer a separate `length` property in the cache entry, so
we do not need to assert that they are in sync.

Closes #54.
Remove Cadence as development dependency.

Don't need it yet. Will probably export it through Proof.

Closes #52.
Remove empty object argument to `report` function.

Removed the empty object argument to `report` function of the tracer.

Closes #55.
Merge branch `simplify-cache` into `master`.