- Add io_error alias for ios::failure [quality karen]

  We currently use the stream type, e.g., ofstream::failure but sometimes
  we work with several streams at the same time which makes it inconsistent.
  So the idea is to add the alias into <*/types> header and use that.

  Alt. names: iofailure, io_failure, ios_failure, io_error, ios_error, but
  io_error would be consistent with system_error.

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