public and private API (still far from ideal, but a start):
* moved several HPKG-classes into the public namespace BPackageKit::HPKG
* added fImpl-wrappers around PackageReader and PackageWriter to hide
most of the gory details
* adjusted 'package'-binary and packagefs accordingly
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@40320 a95241bf-73f2-0310-859d-f6bbb57e9c96