Improve code blocks in documentation

[steffahn]

• some formatting improvements in code blocks
• get rid of most ignored and the should_panic
  • especially the should_panic was confusing IMO, because rustdoc renders it with a huge red bar, (like a deliberately failing example) even though it’s supposed to demonstrate a working app (scaffolding)

[steffahn]

For some reason, running cargo test locally for me only works with f61a01fb7de0db8df6e70fff38e82e469a0a6f1f while CI wants to have d0dcccbaac7229bc0d6ef39b96f2ca4d9d46c700. Both use rustc 1.55.0 (c8dfcfe04 2021-09-06).

[TeXitoi]

Thanks!