Transfer stats @-codes using byte total estimates (e.g. "1.2M")

BTODAY now expands to a byte estimate (DAYBYTES is still the exact byte count)

New codes: UPB and DLB for total-uploaded-bytes and total-downloaded-bytes
There are already existed other codes for kibibytes or exact bytes, but there
were none for byte estimates that shorten larger numbers nicely.

Here's an example of the various transfer stats related @-codes now:

DTODAY:   '1'
BTODAY:   '2.8K'
KTODAY:   '2'
DAYBYTES: '2827'
DLFILES:  '615'
DLB:      '2.2G'
DLBYTES:  '2406384443'
DOWNK:    '2349984'
UPFILES:  '247'
UPB:      '13.6G'
UPBYTES:  '14602185912'
UPK:      '14259947'