Revision exception votes for PRs

[kathrynmohror]

This introduces the concept of a Revision Exception vote, which will allow forward progress on PRs even if minor modifications are made after the quarterly meeting review period deadline or after first vote. If all eligible voting members of the ASC vote 'yes' on the Revision Exception vote, then the PR may proceed for normal voting including the modifications. If any member votes 'no' then the proposer must either re-read the PR with the modifications or proceed to normal vote without the modifications.

[jjhursey]

Please use emoji reactions ON THIS COMMENT to indicate your position on this proposal.

• You do not need to vote on every proposal
• If you have no opinion, don't vote - that is also useful data
• If you've already commented on this issue, please still vote so
  we know your current thoughts
• Not all proposals solve exactly the same problem, so we may end
  up accepting proposals that appear to have some overlap
  This is not a binding majority-rule vote, but it will be a very
  significant input into the corresponding ASC decision.

Here are the meanings for the emojis:

• Hooray or Rocket: I support this so strongly that I
  want to be an advocate for it
• Heart: I think this is an ideal solution
• Thumbs up: I'd be happy with this solution
• Confused: I'd rather we not do this, but I can tolerate it
• Thumbs down: I'd be actively unhappy, and may even consider
  other technologies instead
  If you want to explain in more detail, feel free to add another
  comment, but please also vote on this comment.

[jjhursey]

4Q 2020 ASC Meeting - Oct. 1, 2020

• Passed first vote: 10 yes / 0 no / 0 abstain

[jjhursey]

1Q 2021 ASC Meeting (Feb. 18, 2021)

• Passed second Vote: 9 yes / 0 no / 0 abstain / 5 absent

[jjhursey]

Due to some problems with git on the branch a fresh version of this PR was created in #24