fix(docs): enclose inline code in backticks

[LeoniePhiline]

Fixes #169

Besides enclosing inline code in backticks, I also made two tiny documentation improvements - please let me know if you want them undone:

• In the Report::msg docs, the user is referred to Report::new. I changed this from plain inline code into a link.
• I expanded "Display impl" to "Display implementation", since impl is a Rust token, but
  • "Display impl" looked silly, and
  • "impl Display" disturbed the flow of reading.

[LeoniePhiline]

The CI failures are unrelated: Shall I rebase onto test-ci / #161 / #163?

[yaahc]

@LeoniePhiline I think we'll land 163 then you can go ahead and rebase on master

[yaahc]

turns out I was able to do the rebase myself easily ^_^

[LeoniePhiline]

Thank you! ☺️