v0.3.0

What's Changed

• Replace iterator's back-pointer with previous three-iterator design by @ednolan in #206
• P2728R12 by @ednolan in #207
• Add P3948R1 to references section by @ednolan in #209
• Bump version to 0.3.0 by @ednolan in #208

Full Changelog: v0.2.0...v0.3.0