api: Make the api consistent

When we push data to the tree, we are using prefixed data, but when we verify proofs, we are using non-prefixed data. Whatever the API ends up being, we should probably make it consistent.

This also applies to creating and verifying proofs. When creating proofs, we have two different functions, one for creating a ranged proof, and another for creating a proof to a single leaf. When verifying proofs, we are only using a single function to verify proofs of a single leaf or a range of leaves. Whatever we choose, we should probably make this consistent as well.

relevant comment https://github.com/celestiaorg/nmt/pull/58#discussion_r885091701

related to #55

No files or tests are named. Start by reviewing the tree data-push and proof creation and verification entry points, then read the linked pull-request discussion and related issue #55 to determine the intended consistent API and its completion criteria.

Written by the indexing model from the issue text.