Feature: Taproot support

[bbrtj]

I am looking for volunteers willing to tackle Taproot support. Here is an overview of what works and what not:

• bech32m encoding for the addresses
• P2TR (segwit version 1) output creation and recognition in transactions
• researching tapscripts and what new module dependencies are required to implement them
• implementing Schnorr signatures from BIP340 in Bitcoin::Secp256k1
• signing P2TR outputs via $key->sign (Bitcoin::Crypto::Transaction::Sign needs sign_P2TR method)
• verifying the signatures in Bitcoin::Crypto::Transaction, verify method, BIP342
• adding new SIGHASH as described in BIP118
• adding support for PSBT fields specific to taproot
• adding new key derivation scheme to BIP44, described in BIP86

... and possibly others.

[bbrtj]

I started implementing in feature/taproot branch. Still very much looking for volunteers to implement this.