bsdiff.cc had code to handle both the sub-streams compression and the
patch format. This CL moves the patch file format logic to a new class
in a separated file, and the bzip2 compression to another class. This
allows to replace the core bsdiff logic separatedly from the patch
format.

There are no changes to the functionality of bsdiff and the generated
patches. The code does a bit more of memcpy() since it doesn't write
the control stream to disk as it goes.

Bug: 34220646
Test: Ran bsdiff and compared results with previous version.

Change-Id: Ibdc1482e98cbd370cbed677c326008e19a217ef8