XYZV binary format

Header
DataChunk[]

where Header = {
          char magic[8] {'C', 'E', 'L', 'X', 'Y', 'Z', 'V', '\0' }
          int16_t byte_order /* ALWAYS LE*/
          int16_t digits { 53 } /* std::numeric_limits<double>::digits */
          int32_t reserved { 0 }
          int64_t chunks_number /* -1 == unknown */
      },
      DataChunk = {
          double tdb         /* Julian date (TDB) */
          double position[3] /* x, y, z */
          double velocity[3] /* vx, xy, vz */
      }