Add `log` feature to teensy-panic crate and bump version

[speelbarrow]

The teensy-panic crate documentation says that a log feature may be enabled to have the panic handler output a log message when panicking. This feature was not actually present in the crate's Cargo.toml manifest, this PR adds it to the manifest and bumps the version from 0.2.3 to 0.2.4.

[mciantyre]

I'm not sure the feature needs to be present. The log package is optional. When a dependency is optional, a user can enable it as if it were a feature.

Are you hitting an issue where the feature isn't available / doesn't work on the 0.2.3 release?

[speelbarrow]

Weird. I tried enabling the "log" feature and initially it refused to acknowledge as a valid feature for the package. Now it's working. Who knows 🤷. Closing!