A more efficient way of creating GSS nodes
GSS nodes that only need nonterminal heads and input indices added.
Updating the createGSSNode method
Updating lookup tables.
Removing level-based processing of descriptors from the new branch.
Remaining changes
Meged
The pop method updated.
All test cases pass.
Test case updated.
Another test case added.
Minor changes
Clean up: regular list nodes are removed
pre-computing hash codes and storing them in objects.
Experimenting with an open addressing hash scheme with buckets
Minor update to the hash codes
Option for creating OpenAddressingHashSet with buckets added to the factory.
Some renaming
Moving the hash sets for packed nodes out of non-packed nodes.
Minor changes