encrypt/decrypt/stream API docs are missing new commitment_policy parameter

I was talking with @seebees about this and noticed that the changes to the encrypt/decrypt/stream API parameters was not documented in the docstrings (and thus the rendered API docs).

Locate the encrypt, decrypt, and stream API docstrings and compare their documented parameters with the current commitment_policy argument. Update the missing parameter documentation and verify that the rendered API docs include it for all three APIs.

索引モデルが issue の本文から書いたものです。