v2022.5.3

Major changes includes:

• dropped python 3.6 support
• added support for btclib_libsecp256k1
• the hashes.fingerprint function, removed in the previous version,
  has been reinstated in the to_pub_key module
• encode_num and decode_num have been moved from
  script.op_codes to utils
• op_pushdata and op_str have been renamed to
  serialize_bytes_command and serialize_str_command
• script.op_codes has been removed and its functions merged in script
• script serialization is now more consistent: all integers, even small
  ones, are now considered like bytes. To put small integers on the stack
  OP_X must be used explicitly. Using integers directly will lead to larger
  scripts that will be likely to be rejected by the network as not standard
• check_validity is now correctly propagated inside each function