External access to these functions was removed in #304 when the old
`internals` module and `expose-internals` feature were removed. There
are some valid use cases for them, though (see #351), so let's bring
back a subset of what was in `internals` using the same naming and
documentation conventions that the aes crate uses for its hazardous
functions.
Much of the added or changed documentation is derived from that in
the `aes` crate.
Fixes#351.
Also uses the new `CryptoRngCore` where possible instead of separate
`CryptoRng + RngCore`, and switches to `signature` v2.0.0-pre.3
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
