Update Change Log for 19

Update the change long for draft 18, update acknowledgements

In the acknowledgements section, we want to give @armfazh credit for the
specific improvements he made.

Update the Change Log for draft 17

Add change log update for next draft

Add test vector tests (#548)

* Add tests using test vectors

* Add assertion to front()

* Avoid bare `except`

Update draft-irtf-cfrg-vdaf.md

Co-authored-by: David Cook <dcook@divviup.org>

Don't use SHOULD for gadgets being non-affine

Update Change Log for draft 12

Update change log for draft 11

Update change log