human-readable (-H) option to abbreviate numbers

human-readable (-H) option to abbreviate numbers

Retain 2-3 significant digits and letter n-T for size.  Similar to -h in
ls, du, df, free, rsync, sort; except forgoing byte-specific powers of 1024
in favour of actually _human_ SI powers of 1000.

Common option shorthand -h conflicts with help, but capital -H has a
precedent in df --si so may be more appropriate.