CR support

[plehegar]

Tracked at https://github.com/w3c/echidna/issues/522

[plehegar]

• [x] Support in Echidna https://github.com/w3c/echidna/issues/522
• [ ] new entries in https://github.com/w3c/transitions are notified to Chairs (see https://github.com/w3c/transition-issues-bot)
• [ ] transition requirements updated. See https://github.com/w3c/transitions/issues/63
• [ ] announced to chairs and spec-prod

[plehegar]

THis is also linked to #72

[plehegar]

Updated milestones calculator to support echidna.

[tripu]

(Title should be “CR support”, because support in Echidna is already done, and that's just one part.)