v2020.11.23

Major changes includes:

• updated BIP340 (Schnorr signature) implementation as per the latest changes in bitcoin core
• refactored PsbtIn, PsbtOut, and Psbt
• added legacy sighash
• made btclib compatible with python 3.6
• ssa.det_nonce now returns an int
• moved tagged_hash from ssa into hashes module
• added CurveGroup._y_aff_from_jac and removed unused methods
• discontinued y_odd in favor of y_even as y-simmetry tiebreaker criterium
• removed nonce input from dsa.sign and ssa.sign (only available from _sign functions)
• cleaned up Exception handling, avoided bare/broad except
• introduced btclib Exceptions that can be discriminated from regular Exceptions