* Add mnt6_753 curve
Generalize mnt6 curve model

* Add mnt4 curves

* Use resampled generators

* Calculate correct G2 cofactors

* Add fields to r1cs-std

* Add pairings

* Improve reusing of Fq/Fr among MNT curves

* Add instantiations of curves
Fix Fp6_2over3
Rebase code to current master

* Add test for recursive NIZK proof verification

* Address comments in PR

* Improve test case and port to GM17
Also fix a minor bug in to_field_vec

Co-Authored-By: Pratyush Mishra <pratyushmishra@berkeley.edu>

* Update `digest` and `blake2` requirement from 0.7 to 0.8

Updates the requirements on [digest](https://github.com/RustCrypto/traits) to permit the latest version.
- [Release notes](https://github.com/RustCrypto/traits/releases)
- [Commits](https://github.com/RustCrypto/traits/compare/digest_v0.7.2...digest-v0.8.1)

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Pratyush Mishra <pratyushmishra@berkeley.edu>

* refactor(r1cs-std/boolean): expose enforcing value less than functionality

* fix(r1cs-std/boolean): ensure num_bits is calculated correctly from the arg

* feat(primitives/blake2s): allow creating Blake2s with custom params

* add a pre-commit hook for rustfmt

* make printing sccache stats optional

* fixup! add a pre-commit hook for rustfmt

* Implement CanonicalSerialize/Deserialize improvements

* Improve code readability by using cursor

* Add tests for uncompressed serialization

* Improve serialization size (do not require full u64 limbs to be serialised)

* Change Flags to enum types

* Split up serialization with and without flags.

* Implement simple derive macro

* Derive traits for Groth16 and GM17 keys and proofs