Documentation:
- Add CHANGELOG.md following Keep a Changelog format with complete version history
- Add doc/TAPROOT.md: comprehensive technical specification for BIP340/341/342/350
- Add doc/taproot-guide.md: user-friendly guide for wallet users and developers
- Update README.md: add Taproot highlights, documentation links, and version history
- Add doc/release-notes/release-notes-2.0.0.md
- Update doc/bips.md with Taproot BIP entries (340, 341, 342, 350)
- Remove standalone doc/release-notes.md (replaced by versioned directory)
Documentation covers the complete Taproot implementation backported from
Bitcoin Core v24.2, including Schnorr signatures, bech32m addresses,
and BIP9 deployment timeline for mainnet activation (March 2026-2027).
CHANGELOG.md contains detailed history from v1.1.0 to v2.0.0 with real
commit information extracted from GitHub repository tags.
