Btclib

Major changes includes:

- dropped python 3.7 support

This is the last release supporting py37.

Major changes include:

- added first draft implementation of descriptors
- added first draft implementation of script engine
- added taproot psbt fields
- improved bip32 derivation (speeded-up, added one more test)
- supported py3.12 with btclib_libsecp256k1
- updated toolchain

Major changes include:

- Fix circular import between ``script`` and ``b32``

Major changes include:

- enabled libsecp256k1 by default
- improved documentation
- used generic containers (Sequence instead of list, Mapping instead of dict)
where possible

Major changes include:

- exported names per module (bip32, block, ec, ecc, mnemonic, psbt, script, tx)
- added join_psbts and join_txs
- refactored bip340_nonce
- improved integration of libsecp256k1
- added secp256k1-py test vectors
- improved typing
- added SECURITY, CONTRIBUTING, bug report and feature request templates
- added pre-commit hooks
- adopted *mypy --strict* and *from \_\_future\_\_ import annotations*

Major changes include:

- add support for PSBT's taproot fields (bip370)
- added support for Python 3.11
- fixed the OpenSSL 3.x RIPEMD160 issue in btclib/hashes.py
- added CONTRIBUTING and SECURITY
- solved issue 73
[Re-import Tx subclasses into btclib.tx](https://github.com/btclib-org/btclib/issues/73)