byte-count to string routines type unsigned 64-bit int now

We don't have a use case negative byte values in strings anywhere that I can think of.

Created wrapper for MSFT _ui64toa_() - unsigned 64-bit integer to ASCII string.

Add Petabyte (actually, Pebibyte) support to byte_count_to_str()  and byte_estimate_to_str().

Removed 'B' suffix from byte_estimate_to_str() output for values < 1024. Callers may display this returned string followed by "bytes" (or similar) and thus the 'B' suffix is redundant in that case. If the caller needs a 'B' suffix, they can detect no suffix and add it.