Misleading interface description

[andrewdavidsmith]

(from @Alexandra2022kzn original issue)

I also tried changing the input memory buffer size with --mem, but noticed that the verbose output always reports:

input memory buffer size: 1MiB

For example, both -m 64M/-m 1G still report 1MiB. Also, -m 256MiB is rejected with:

--mem: mib unit not recognized. Allowed values: {g,k,m}

although the help message shows the default as 256MiB.

[andrewdavidsmith]

This interface issue should be fixed with PR #135

I want to allow upper and lowercase for the letter (g/m/k), but that won't make sense for the "B" since it has different meaning. So it will only work with upper/lower G/M/K but now the help message is fixed to reflect that, and the verbose output is also changed to be consistent.