Function: file-size-human-readable

Produce a string showing FILE-SIZE in human-readable form.

Optional second argument FLAVOR controls the units and the display format:

If FLAVOR is nil or omitted, each kilobyte is 1024 bytes and the produced
suffixes are "k", "M", "G", "T", etc.
If FLAVOR is `si', each kilobyte is 1000 bytes and the produced suffixes
are "k", "M", "G", "T", etc.
If FLAVOR is `iec', each kilobyte is 1024 bytes and the produced suffixes
are "KiB", "MiB", "GiB", "TiB", etc.