This commit moves the previous implementation of `SparseMerkleTree` from
miden-core to this crate.

It also include a couple of new tests, a bench suite, and a couple of
minor fixes. The original API was preserved to maintain compatibility
with `AdviceTape`.

closes #21

closes #5

Currently the API modules are hidden to the crate scope.

In order to avoid global permissive allows, they can initially be
exported, and tweaked to local scopes as they get implemented, finalized
and tested.

Related to #3