Rebuilds the hash table.
The member function alters the number of buckets to be at least _Buckets and rebuilds the hash table as needed. The number of buckets must be a power of 2. If not a power of 2, it will be rounded up to the next largest power of 2.
It throws an out_of_range exception if the number of buckets is invalid (either 0 or greater than the maximum number of buckets).