new: Add colored log levels

[camnwalter]

Closes #905
Also see hermit-os/loader#336

[mkroening]

Thanks a lot for the PR! :)

This is great, but I have a few visual and technical requests:

Visual requests:

1. I think we should only color the level (e.g., WARN in [WARN]) and not the whole line.
2. For color choice I would prefer if we would follow what tracing-subscriber is doing: tracing-subscriber/src/fmt/format/mod.rs#L1504-L1510
3. We should respect the NO_COLOR environment variable at build time to disable any colors.

Technical requests:

I think it would be good, if we introduced a newtype ColorLevel(Level) that implements a colored 'Display' via anstyle.

[camnwalter]

I think it would be good, if we introduced a newtype ColorLevel(Level) that implements a colored 'Display' via anstyle.

anstyle comes with the stdlib, so do you want me to re-create what they do?

[mkroening]

anstyle comes with the stdlib, so do you want me to re-create what they do?

If you disable the default std feature, it should work:

anstyle = { version = "1", default-features = false }

[mkroening]

Thanks, this is looking great. Could you remove the explicit types from the let bindings unless necessary? :)

[mkroening]

Thanks! :)

[camnwalter]

No problem! I'll do similar changes in the other pull request in a little bit