Milestone planning for 1.0.0 and post-1.0.0

[ajnelson-nist]

The 0.20.0 release notes indicate 0.20.0 is a release candidate for 1.0.0.

I think there are some Issues and PRs present worth issuing another release before 1.0.0. There may also be some things comfortably doable between 1.0.0 and 2.0.0.

It would be helpful to know what is on the project maintainers' roadmap, especially if a new feature is believed to be a backwards-incompatible change. Would the maintainers be interested in defining a few milestones:

• 1.0.0
• 1.x.0 (all issues and PRs believed backwards-compatible with 1.0.0)
• 2.0.0 (all issues and PRs believed backwards-incompatible with 1.0.0)