converters: Add conversions of computer data units

[XargsUK]

It would be useful to be able to convert computer data units. Here are the ones that I would find useful:

bit
byte
kilobit
kilobyte
kibibyte
megabit
megabyte
mebibyte
gigabit
gigabyte
gibibyte
terabit
terabyte
petabit
petabyte