Deprecate env_logger::from_env and clean up examples

[KodrAus]

The env_logger::builder and env_logger::from_env methods are a bit confusing as-is, because it's not clear that env_logger::builder should call Builder::from_default_env instead of Builder::new. The builder function is a convenient way to get started configuring your logger before initializing it, but the from_env method doesn't actually save you any work because you still need to use env_logger::Env, so may as well use env_logger::{Builder, Env} while you're at it.

I've also cleaned up our examples a bit and added a new one for logging in cargo test.

[mainrs]

Lint is unrelated to the PR.

[KodrAus]

I'll fix up that lint while I'm here.

[mainrs]

I'll fix up that lint while I'm here.

Started on #169. Some more popped up after that. You should be able to push to that Pr since you’re maintainer.

[mainrs]

Anything you want to add to the PR @KodrAus? Else this can be merged.