Since Criterion can only benchmark public API, these changes just drop
all internal benchmarks (e.g., benchmarks for field operations). But
those are usually microbenchmarks whose meaning is kind of questionable
anyways, so I don't think this is a big loss.
The `bench` feature disappears, since Criterion works on stable Rust.
As noted in the Decaf paper, mapping twice and adding the results ensures a
uniform distribution over the group. This changes our random point and
hash-to-point functions to do this, matching the Sage script.
This allows iterators returning either &Scalars or Scalars, so that it's
possible to use map() and friends to adjust scalars as they're being fed into
the multiscalar multiplication.
The public-facing types with arithmetic operations are:
- `Scalar`s
- `ExtendedPoint`s
- `RistrettoPoint`s
For these types we define operators with all combinations of borrowed and
non-borrowed inputs, to avoid forcing API consumers to write extra ampersands.
Since all of the operations involved with these types are expensive relative to
the cost of an unnecessary copy, this isn't a big deal.
The `MontgomeryPoint` struct isn't included in the above because it's only
useful for scalar multiplication.
This commit is based on work by @UnlawfulMonad.
