Line Numbering -- remove leading space; and, customize trailing character.

[Keith David Bershatsky]

I am uncertain whether this issue has already been discussed ad nauseam, either 
when built-in line numbering first came out or sometime thereafter, but here 
goes anyway ...  In a recent thread on emacs.stackexchange.com, a user did a 
comparison screenshot between the new built-in line numbers and the old ones 
that were generated via Lisp.  In that thread, the user wondered what could be 
done to shrink the width of the built-in line numbering ...

https://emacs.stackexchange.com/questions/52269/how-to-change-line-number-gutter-width-using-display-line-numbers-mode

I posted an answer pointing the O.P. to the variable 
`display-line-numbers-width' and its doc-string.  In addition, I made reference 
to the two lines in maybe_produce_line_number responsible for the left/right 
space padding surrounding the line numbers.

All of that got me thinking ... how would it look if I removed the leading 
space and changed the trailing space into a "|" symbol?  Attached is a 
screenshot of what this looks like ...

Have there been some requests to customize the leading/trailing spaces, and, if 
so, what was the consensus?  If not, then it may be something worth considering 
....  I think the attached screenshot looks kind of nifty, and saves me 11 
pixels of screen real estate after eliminating one character (the space) on the 
left, which happens to be my frame-char-width ...