The problem with std::collections::HashMap is that there is no core::collections::HashMap or similar replacement for our no_std environment.
Also hashbrown seems to have superior performance.

This will help writing tests with general setup and tear-down mechanics.
Used to initialize env_logger for every unit test.

Fixed now!

The new system uses similar patterns as .gitignore does.

This should make it work in a default test environment.

This enabled TestEnv and disabled DefaultEnv.
Use this for testing.
Before this commit the standard "test" feature was used, however, its problem is that the test feature is crate-local and cannot be enabled or disabled by dependencies.