- Rename disfigure to deconfigure [quality]

  Another alternative is unconfigure. Wonder if rename or add/keep alias.

- Can we use consts instead of macros for versions [quality]

  And use static_assert() to check. This will be required to transition to
  modules (current thinking says modules don't "leak" macros).

- Remove build2 repositories from scm.codesynthesis.com [infra]