Add error checking to getsector
Format the file with recent changes
Remove padding field, no longer needed for on-disk binary compatability.  Change sector to a class
Change getsector to return a unique_ptr to newly allocated memory.  move now works without any null pointer dereferences on the sectors.  putsector and other sector consumers now take either a const reference or a regular reference since the pointer can't be easily handed in and I wanted to catch mistakes like consumers freeing the pointer