Rename BBlockBufferCache and friends to *Pool*

Also move BBlockBufferPoolNoLock into BHPKG namespace with the other
classes. Not sure why it wasn't there before.

package kit: internalize BPackageDataReader

It is no longer public (or even private) API. BPackageDataReaderFactory
returns a BAbstractBufferedDataReader instead. The advantage is that
the latter doesn't have hpkg format specific dependencies.

BPackageDataReader: Remove unused Size(), BlockSize()

Clone read support functionality for HPKG format version 1

It uses sub-namespace BPackage::BHPKG::V1. Unlike the one for the
current format version, the V1 version of BPackageInfoContentHandler
lives in BHPKG(::V1) sub-namespace and is private.

Rename BBlockBufferCache and friends to *Pool*

Also move BBlockBufferPoolNoLock into BHPKG namespace with the other
classes. Not sure why it wasn't there before.

package kit: internalize BPackageDataReader

It is no longer public (or even private) API. BPackageDataReaderFactory
returns a BAbstractBufferedDataReader instead. The advantage is that
the latter doesn't have hpkg format specific dependencies.

BPackageDataReader: Remove unused Size(), BlockSize()

Clone read support functionality for HPKG format version 1

It uses sub-namespace BPackage::BHPKG::V1. Unlike the one for the
current format version, the V1 version of BPackageInfoContentHandler
lives in BHPKG(::V1) sub-namespace and is private.