Improve site formatting (#2183)

* Improve site formatting

- Separate titles with blank lines
- Separate code blocks with blank lines
- Always use ``` blocks for examples
- Use console for console (bash syntax highlighting does work well with
  example command output)
- Start console examples with $ (highlight command and output
  differently and more friendly to other shells users)

* Unify indentation in example project structure

* Use single import line in the trivial examples

When we want to show a minimal example with single import it looks
cleaner and more minimal with a single line.