Currently we have a few problems with our feature gating, attempt to
audit all feature gating and fix it by doing:
1. Do not enable features on optional dependencies (`rand` and
`bitcoin-hashes`) in dev-dependencies, doing so hides broken feature
gating in unit tests.
2. Do not use unnecessary feature combinations when one feature enables
another e.g. `any(feature = "std", feature = "alloc")`.
3. Enable "std" from "rand-std" and "bitcoin-std" (and fix features
gating as for point 2).
4. Clean up code around `rand::thread_rng`, this is part of this patch
because `thread_rng` requires the "rand-std" feature.
5. Clean up CI test script to test each feature individually now that
"rand-std" and "bitcoin-hashes-std" enable "std".
Run the command `cargo +nightly fmt` to fix formatting issues.
The formatter got confused in one place, adding an incorrect
indentation, this was manually fixed.
In multiple places we use array constants for zero and one. Add two
constants and use them throughout the codebase. Note the endian-ness of
`ONE` in the docs.
This adds `Scalar` newtype to better represent values accepted by
tweaking functions. This type is always 32-bytes and guarantees being
within curve order.
Tobin C. Harding
Martin Habovstiak