SI prefixes with "accepted" units, others

I've started work on making MathCAT handle ":units" and wonder how many of
the "accepted" units (and others?) should or should not take SI prefixes
(kilo, penta, ...). The units that we came up with are listed in issue #475
<https://github.com/w3c/mathml/issues/475>.

For example, does "kh" for "kilo-hour" make any sense? "kt" for
"kilo-tonne"? "kl" for "kilo-liter" does make sense though ("liter", or for
the British "litre", is not a base unit, it is an accepted unit).

Make sure to look at the "other" category at the bottom. Some of them such
as bytes and calories take a prefix.

Thanks for any guidance you can provide. For posterity, adding your
thoughts to the issue would be best, but feel free to reply to this email
if that is much easier for you.

    Neil