Add batv-keygen script for generating BATV key
milter: zero out private data with smfi_setpriv after freeing it

This shouldn't matter but libmilter was logging a warning because we
weren't doing it.
Add README and initial documentation
Rearrange some docs
Add NEWS file, release version 0.3
Add missing includes
Release 0.4
Merge branch 'master' into debian
Update debian packaging for 0.4 release