feat(cargo): Style help like cargo nightly

[epage]

As of rust-lang/cargo#12578, nightly cargo's help has terminal styling applied to it. This PR updates cargo-fmt to match so commands that appear built-in to the user all behave the same.

Other differences not address

• Help headings
• A footer recommending to run cargo help fmt (and providing an accompanying man page to be shown instead)

See rust-lang/cargo#12578 for screenshots of cargo and cargo run with different themes.

[calebcartwright]

lgtm, like the short and sweet ones!

@ytmimi - i can't recall the specifics but vaguely remember a semi-recent case where some change did something odd to our terminal coloring that you investigated. i'll defer merging this to you accordingly on the off chance there's anything you want to consider based on that (if not then feel free to bash the merge button!)

[ytmimi]

Updated output looks good to me, thanks!