Merge branch 'sp/indexpackv2'
* sp/indexpackv2:
Default IndexPack to honor pack.indexversion configuration
Add support for writing pack index v2 files
Compute packed object entry CRC32 data during IndexPack
Add 64 bit network byte order encoding to NB
Reuse the magic tOc constant for pack index headers
Refactor pack index writing to a common API
Document PackedObjectInfo and make it public for reuse
Rename ObjectEntry to PackedObjectInfo
Make ObjectEntry's position field private
Extract inner ObjectEntry from IndexPack class