Release v0.3.1

Changed

• Update Makefile (and the called testing/setup_testenv.sh script) to allow
  for providing a custom location for generation of test files)

Fixed

• Minor tweak to logging output to reduce duplication between main log message
  and the structured field

References

• See the v0.3.1 milestone for the issues associated with this release.
• See our CHANGELOG for more information