add some type descriptions
add some command line arguments parsing capability
check if the vhd exists before trying to open it
add documentation
misc re-indent
use the cheaper newtype to wrap sector and data.
prevent re-defining bits from Data.Bits by using a different symbol
add support to extract only a range of data
add block data mapper layer to handle encryption (AES-XTS-Plain).

reshuffle types to use newtype more often (and thus be much safer).
lot of kludge to have better code at the expanse of the diff.