Address most of Ben Kaduk's comments

[huitema]

After that, there are only very few points left to address in Ben's comments (issue #158).

[huitema]

@kaduk you may want to take a look at these changes, and also at the discussion in issue #156. The changes are in complement to Pr #158 that clarified that 0-RTT support is optional, and other PRs that addressed most of the IESG review comments.

[kaduk]

Thanks, this looks good.
(I guess whether or not trailing whitespace is to be avoided is a matter of local policy.)

[huitema]

@saradickinson please check my latest changes, and see whether that resolves your concerns.

[saradickinson]

@huitema yes - thank you!