This is a 🙋 feature.

Overview

The general rationale for this is documented in #48.
This PR implements the required behaviour. A human-panic
message will only be displayed if two conditions are met

1. The program is not running in DEBUG mode
2. RUST_BACKTRACE is not set as an env variable

This PR also adjusts the tests to check for both present
and non-present human-panic messages.

There are two things missing

• Properly document this change!
• A test that checks for the RUST_BACKTRACE override
  behaviour when running in RELEASE mode. This is currently
  not easy to do with assert_CLI (there might be more PRs 🙂)

Checklist

• tests pass
• tests and/or benchmarks are included
• documentation is changed or added

Semver change

Now, this is a matter of how you define a version breakage.
SemVer is ambigous when it comes to what is and isn't a breakage,
for example, if people are depending on human-panic messages to be
present to parse things from logs then any tool that updates
human-panic while we are changing behaviour will break.

In the code, this is at most a minor bump. But seeing as we're
also looking at things to add for a 2.0 release, we might want to
put it on the tracking issue (#46).

Either way, we need to document this change because it might have
a large impact on people who depend on the stdout message to be
present.