byte[] for
   the termNumber lists, or directly contains the termNumber list if it fits in the 4
   bytes of an integer.  If the first byte in the integer is 1, the next 3 bytes
   are a pointer into a byte[] where the termNumber list starts.

   There are actually 256 byte arrays, to compensate for the fact that the pointers
   into the byte arrays are only 3 bytes long.  The correct byte array for a document
   is a function of it's id.

   To save space and speed up faceting, any term that matches enough