docs: rewrite the 2.0 release log new-API-first and complete the audit

The 2.0.0 section documented only locale packs and a machine-generated
behavior-diff draft. It never mentioned that 2.0 introduces a new API,
and listed none of the removals -- a reader upgrading met the ma/do
acronym data change before learning parse() exists.

Restructure into: orientation paragraph, The 2.0 API, Breaking Changes,
Behavior Changes, International name support, Compatibility layer,
Command line, Documentation. Same shape 1.3.0 already uses, scaled up.

Audited against the v2.0 milestone and all 218 branch commits. Adds the
previously undocumented removals (#223, #243, #245, #255, #256, #257,
#258, #261, #268, #279, #280), the new API surface, the Python 3.11
floor, the CLI rewrite, and the docs rewrite.

Two removals are called out as silent breaks, since neither raises:
HumanName == str flipping to False (#223), and the 1.3.1-documented
CONSTANTS.regexes.bidi = False opt-out now raising.

Drops the per-bullet cases.py row citations and differential-corpus
qualifiers -- they serve the author, not the reader -- and folds the
harness explanation into one closing note.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: derek73