Update Nushell Book with copy-able examples.

[0x4D5352]

Based on Issue #1684. I've left two sections in the book unchanged pending additional comments:

1. how_nushell_gets_run.md - the REPL section specifically calls out the prompt indicator > .
2. overlays.md - Lines 63-66 specifically call out the indicator and the overlay prefix.

In some cases, I added the # => prefix to example outputs that were not attached to a command example with a > prefix to maintain consistency across examples, unless the example output was presented in isolation. However, I may have missed some instances.

[0x4D5352]

As per @NotTheDr01ds comment in the issue, I'm keeping any instance of the prompt where it's explicitly called out as part of the example.

[0x4D5352]

Noticed that there was still a page in both Spanish and Portuguese for the deprecated shells command, removing them as per a conversation in Discord.

[NotTheDr01ds]

Wow! Thank you for this cleanup!

I've caught a few things that the search/replace didn't quite seem to handle quite right.

Unfortunately, I could only review up to about halfway through the Spanish book before my browser crashed due to (I'm guessing) the length. We might need to split PRs like this up into smaller chunks :-)

[NotTheDr01ds]

The review comments might not have appeared last night because of the browser crash. Resubmitting.

[0x4D5352]

@NotTheDr01ds Indentation's been fixed; the "When does $in change" list has also been conformed to the same style throughout. Between that and your smaller suggested fixes, this should be good to go.

[NotTheDr01ds]

Thanks! Merged! (Again) Great cleanup!