Increase max hash size to 64GB

Now that TT cluster ize is 32bytes and
we address TT table by cluster, it is
possible to raise the limit to 64GB
while still using a uint32_t to index
the cluster within teh table.

No functional change.

src/ucioption.cpp

@@ -60,7 +60,7 @@ void init(OptionsMap& o) {
   o["Contempt Factor"]          << Option(0, -50,  50);
   o["Min Split Depth"]          << Option(0, 0, 12, on_threads);
   o["Threads"]                  << Option(1, 1, MAX_THREADS, on_threads);
-  o["Hash"]                     << Option(32, 1, 16384, on_hash_size);
+  o["Hash"]                     << Option(32, 1, 65536, on_hash_size);
   o["Clear Hash"]               << Option(on_clear_hash);
   o["Ponder"]                   << Option(true);
   o["MultiPV"]                  << Option(1, 1, 500);