Builder for a data store that is backed by a java.nio.MappedByteBuffer. This has a limitation that the total size of the mapped buffer and therefore the hash table can not exceed 2 gigs.

The data store file has the following structure.

 file: header, hash table, nameArray, nameTable, hitTable

 header:
   int hashTablePos, // byte offset in file
   int hitTablePos,  // byte offset in file
   int nameArrayPos, // byte offset in file
   int nameTablePos, // byte offset in file
   int wordLength,
   int serializedPackingLength,
   byte[] serializedPacking

   hash table:
     int hashTableLength,
     int[hashTableLength] hits // index into hitTable

  nameArray:
    int nameArrayLength,
    int[nameArrayLength] nameRecord // byte offset into nameTable

  nameRecord:
    int nameTableOffset
    int sequenceStartOffset
 
  nameTable:
    int nameTableSize, // size in bytes
    (short nameLength, char[nameLength] name)[nameTableSize] names

  hitTable:
    int hitTableSize, // size in bytes
    hitTableRecord[hitTableSize] hits

  hitTableRecord:
    int hitCount,
    hitRecord[hitCount] hit

  hit:
    int offset    // offset into the sequence