Some classes such as DiskAdaptor, DiskWriter, FileAllocationIterator and ChecksumValidator are left unchanged.
Since off_t is int64_t with LFS, we cannot take advantage of extra capacity of uint64_t.
Added .cc file for classes/structs that only provided by header file. Defined non-POD classes' ctor, dtor in .cc file. Moved implementation code in header file to .cc file for major classes/strucsts.