Release v0.4.0

Added

• Latest Release badge on README
• Support for environment variables via alexflint/go-arg package
• Makefile
  • command: testrun
  • Set version global variable in main package based on git describe

Changed

• --extension (multi-use) flag is now --extensions (single call, multiple values supported
  • See README for usage
• Replaced jessevdk/go-flags package with alexflint/go-arg
• Improve configuration validation to accommodate lack of native go-arg
  support for enforcing specific flag values
• Makefile
  • TODO: Add more info here
• go.mod updated to use Go 1.13 as the base version
  • Based on some reading in https://github.com/golang/go/wiki/Modules, the
    behavior for go get -u changed to allow more conservative updates of
    dependencies. The new behavior sounds more natural and is less likely to
    surprise newcomers, so locking the base behavior to Go 1.13 sounds like a
    "Good Thing" to do here.
• README updated to note Go 1.13 as the base version

Removed

• jessevdk/go-flags package replaced with alexflint/go-arg

Fixed

• Typo in license text
• Replace lightweight Git tags with annotated tags

References

• See the v0.4.0 milestone for the issues associated with this release.
• See our CHANGELOG for more information