Release v1.5.0

Added

• Serialization & Sanitization: Introduce additional serialization contexts, and update docs to talk about the importance of putting your sanitized content in the right context (see docs/sanitization.md).

Changed

• Sanitization: Switch the sanitizer pipeline to be built up entirely of basic transform blocks (see docs/transforms.md).

Changed

• Tokenizer: Add fast-path handling for tag names and attribute parsing to reduce overhead in common cases.
• Sanitization: Speed up URL normalization and scheme validation while preserving policy semantics (see docs/url-cleaning.md).
• Transforms: Optimize sanitizer transform dispatch and attribute rewrite hot paths for lower per-node overhead (see docs/transforms.md).