quotation characters in the Octave sources

[John W. Eaton]

Recently I've noticed the use of various characters for quotation marks 
in the Octave sources, including ASCII apostrophe, grave accent, acute 
accent, and Unicode left/right single quotation marks.  I'd like to come 
up with a uniform guideline for these characters, fix the sources, and 
try to stick with it in the future.

A complete discussion of the issue may be found here

  https://www.cl.cam.ac.uk/~mgk25/ucs/quotes.html

Briefly, in the old days, we used `' (ASCII grave and acute accents) 
when surrounding words with single quote characters.  It wasn't correct 
usage, but they were displayed by X11 as left/right single quotation 
characters and I think Texinfo also displayed them as matched quotation 
characters, so they appeared to be the right thing and were easily 
accessible characters on US/ASCII keyboards.  But then X11 changed and 
these characters are now displayed (correctly) as grave accent (slanted) 
and apostrophe (neutral) so in addition to being the wrong combination 
of characters, they look terrible together.

Once that change was made, I think we started simply using the ascii 
apostrophe character like 'this'.  I'd like to fix the sources to use 
that convention again.  Does anyone object or have a better suggestion? 
No matter what we decide, I'd like to have consistent usage in the 
source files.

jwe