Merge pull request #566 from ampproject/main

Snapshot version 8 from main.

Merge pull request #531 from ampproject/master

Release version 7 of AMP cache transforms

Merge pull request #511 from ampproject/master

Snapshot release version 6.

Merge pull request #481 from ampproject/master

Snapshot release v5

Merge pull request #460 from ampproject/master

Snapshot release v4

Merge pull request #386 from ampproject/master

Snapshot release v3

Merge pull request #321 from ampproject/master

Snapshot version 2 from master.