Rewrite to support locale-specific

Rewrite to support locale-specific
notations like thousands separators.
Specify what includer of include.h must include beforehand.
(human_group_digits, human_suppress_point_zero, human_autoscale,
human_base_1024, human_SI, human_B): New enum values.
(human_readable): Rename from human_readable_inexact; put the
options before the sizes.  All uses changed.  The old human_readable
function has been removed; use inttostr.h instead.
(human_options): Renamed from human_block_size, with new signature
that allows block sizes up to UINTMAX_MAX.  All callers changed.