Python SortedSet for platforms without blist

Fixes PYTHON-104
Fixes PYTHON-167
Addresses CASSANDRA-8030

For nested UDTs and collections, the set we return must accommodate
non-hashable objects (built-in set does not).
Change to 'sortedset' to match cqlsh type mapping.

also made eq, ne comparisons more robust for other types
Copy internal ist for sortedset::copy
Merge pull request #200 from datastax/PYTHON-167

Python SortedSet for platforms without blist