Add parser for DRBD /proc file

A new directory for haskell modules about block devices has been created
The parser is divided in two modules:
* one exports the data types describing the DRBD status
* one exports the parser itself

Signed-off-by: Michele Tartara <mtartara@google.com>
[iustin@google.com: indentation/alignment fixes]
Reviewed-by: Iustin Pop <iustin@google.com>