[scrape] multiline description of options aren't scraped properly

[ildar]

$ echo "
  --allow-untrusted     Install packages with untrusted signature or no
                        signature
" |  complgen scrape
 | --allow-untrusted "Install packages with untrusted signature or no"

i.e. second line is cut off.

I'd propose:

1. fixing the issue shown above
2. (ideally) add an option to cut off the description beyond the 1st dot (.) Then the description would be just the 1st sentence of the full help.

Then the scd docs could be parsed automatically.