Remove support for VMS.
Remove support for DOS.
Remove files we do not need anymore.
Remove binaries for win32.
Update ISBN and ISBN-13 handling.

Instead of relying of a specific field (isbn-13 or isbn) to choose
the proper checking function, we now choose the correct one by
looking the first three digits of the field: if it starts with 978,
it's a ISBN-13, otherwise ISBN.

I also update the validation function for both ISBN, invalidating
numbers that have fewer digits than required.

Some minor cleanups were also made. For instance, I removed all
K&R declarations. Some comments regarding functions were also
written 'javadoc' style too.