v0.8.0-alpha.20

What's Changed

• Implement try_transmute_{ref,mut} by @jswrenn in #1622
• Reorganize macro modules under util module by @joshlf in #1623
• Module reorg finish by @joshlf in #1624
• [README] Link to 0.8 alpha draft release notes by @joshlf in #1625
• Release 0.8.0-alpha.20 by @google-pr-creation-bot in #1626

Full Changelog: v0.8.0-alpha.19...v0.8.0-alpha.20