This was a bit stuffy and verbose, so try to make it a tad more human.
Also don't mention `fish_opt` constantly. It's not actually all that
useful as argparse isn't as difficult to use as we thought.
[ci skip]
Adds synopses for those commands missing them.
Moves all synopsis sections to code blocks. This improves the appearance, although highlighting as
fish code may not be the ideal appearance.
This keeps all unknown options in $argv, so
```fish
argparse -i a/alpha -- -a banana -o val -w
```
results in $_flag_a set to banana, and $argv set to `-o val -w`.
This allows users to use multiple argparse passes, or to simply avoid
specifying all options e.g. in completions - `systemctl` has 46 of
them, most not having any effect on the completions.
Fixes#5367.
