Changes

* A Close table can trade some speed for compactness, but it seems to be a bad bargain:

** The load factor is adjustable. (The hash table size must remain at a power of two, but the data vector can have non-power-of-2 sizes.) However, increasing the load factor directly affects LookupMiss speed.

** An implementation could grow the data array by less than doubling it each time. I tried this. Insert speed suffered; lookup speed was unaffected; but the modified CloseTable still used more memory than OpenTable.