[saitakarcesme]

Fixes #432.

Document how to assign tag_callback on an HTML2Text instance, its four arguments, and the exact True return value that bypasses default tag handling. Include an executable example that removes bold formatting while preserving the enclosed text and other tags, and explain how to restore default handling. Update the changelog and author list as requested by the contribution guide.

Validation on macOS / CPython 3.13.5:

• Extracted and executed the example from docs/usage.md; its output assertion passes.
• Checked opening/closing callback arguments, nested italic content, and resetting the callback to None against the current implementation.
• Full pytest suite: 196 passed (3 PytestRemovedIn10Warning notices about existing generator parametrizations), 87% coverage with --cov=html2text.
• git diff --check passes. No runtime code changed.

Prepared and validated with AI assistance (OpenAI Codex).

[saitakarcesme]

CI follow-up: CI — status: action_required on the current head 2192c2e. These fork workflow runs have not started. Could a maintainer approve them so the change can be validated?

Status checked and follow-up prepared with Codex assistance.