Interfacing with Python, part 2

[fjarri]

Based on top of #45

Bringing Rust in sync with nucypher/pyUmbral#267

• added Signer class
• exposed Signature class with recovery_flag() method
• take signer instead of a secret key in generate_kfrags()
• split SerializableToArray into serialization and deserialization traits - some types (like verified kfrags and cfrags) can only be serialized.
• implemented the new forced verification scheme for kfrags and cfrags
• exposed CurvePoint and CurveScalar (since they are returned by verification_kit(), and exposed as fields as well)
• added CapsuleFrag.verification_kit()
• exposed Capsule and CapsuleFrag fields for verification purposes
• added CurvePoint.to_affine() returning a pair of serializable coordinates
• bumped dependencies, and set MSRV=1.51 (bounded by heapless)

[codecov-commenter]

Codecov Report

Merging #47 (81bc70f) into master (d70d6ae) will decrease coverage by 0.38%.
The diff coverage is 89.63%.

@@            Coverage Diff             @@
##           master      #47      +/-   ##
==========================================
- Coverage   94.98%   94.59%   -0.39%     
==========================================
  Files          11       11              
  Lines         777      814      +37     
==========================================
+ Hits          738      770      +32     
- Misses         39       44       +5     

Impacted Files	Coverage Δ
umbral-pre/src/dem.rs	92.50% <ø> (ø)
umbral-pre/src/traits.rs	96.42% <ø> (ø)
umbral-pre/src/capsule_frag.rs	94.48% <81.08%> (-0.60%)	⬇️
umbral-pre/src/key_frag.rs	88.50% <83.33%> (-0.74%)	⬇️
umbral-pre/src/hashing_ds.rs	92.00% <87.50%> (-8.00%)	⬇️
umbral-pre/src/capsule.rs	99.06% <100.00%> (+0.02%)	⬆️
umbral-pre/src/curve.rs	94.11% <100.00%> (+2.11%)	⬆️
umbral-pre/src/hashing.rs	97.14% <100.00%> (-0.73%)	⬇️
umbral-pre/src/keys.rs	95.87% <100.00%> (+0.52%)	⬆️
umbral-pre/src/pre.rs	100.00% <100.00%> (ø)

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[piotr-roslaniec]

LGTM 🎉

[fjarri]

I'll wait a little before merging pending the results of today's meeting. It may be possible we don't need the Adjudicator-specific API after all.