Update documentation for dupload and dput

Update dupload features, and by extension dput by way of reference to dupload. Remove old differences that have been supported by dupload for a long time such as checking the OpenPGP signatures and checksums for .changes files. Keep the dinstall mention which can be implemented via a hook in dupload, but is not supported out of the box.

Signed-off-by: Guillem Jover guillem@debian.org