Introduce stable arithmetic to avoid nightly/unstable features for some platforms
This PR allows the user to opt-out of the "u128-support" feature so that they can use the stable compiler and avoid the unstable `i128_type` feature in the Rust compiler. (Pass `--no-default-features` to opt out.)
This roughly triples the cost of everything in my experience, but it's necessary on some platforms (`arm-linux-androideabi`) which Rust/LLVM doesn't compile 128-bit integers for correctly yet.
**Before this can be merged the CI needs to test against this being enabled or disabled.**
s/is_in_correct_subgroup/is_in_correct_subgroup_assuming_on_curve/
I added a new method`is_in_correct_subgroup_assuming_on_curve` and added the method `is_in_correct_subgroup` for the `CurveAffine` trait.
Group encoding negative test vectors
Closes#10
Also simplifies the encoding code, which has the side-effect of being useful for testing. Also adds more descriptive error reporting throughout the API. Also ensures use of Debug/Display are consistent with standard expectations.
bmerge