Improve code/comment/output markings & display consistency

This PR aims to increase the consistency across the docs for
codeblocks and code/comment/output markings.

Rule followed here is "what's visible on the screen should be reflected"

> Please note:
> Due to a vast amount of items reviewed and changed for this PR, there
> might be some individually incorrect replacements OR patterns of incorrect
> replacements. This PR needs to be reviewed and if there is anything missing,
> it should be improved or amended.

Closes:
https://github.com/dotcloud/docker/issues/5286

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)