* Clear cofactor in BN254 G2 testgen and frobenius
* Implement G2 endomorphism acceleration in Sage
* Somewhat working accelerated scalar mul G2 (2.2x) faster
- OK for BN254_Snarks
- Some test failing for BLS12-381
* Fix negative miniscalars by adding an extra bit of encoding
* Cleanup accel params
* Small recoding optimizations