Use test_log::test to have env logging in all tests

[obsoleszenz]

To enable logging in tests one can now simply use the RUST_LOG=trace environment variable.

Example:

RUST_LOG=trace cargo test --features log

Also added the log feature to Cargo.toml, i think it's cleaner to list all features explicitly.

[HEnquist]

This looks pretty neat. Would it be possible to have the logging enabled automatically when running the tests? Enabling the log feature works of course, but it would nicer to not need to do that.

[obsoleszenz]

This looks pretty neat. Would it be possible to have the logging enabled automatically when running the tests? Enabling the log feature works of course, but it would nicer to not need to do that.

Sadly cargo doesn't support this yet https://github.com/rust-lang/cargo/issues/2911