Support for long indices

[mikera]

With the new sparse matrix support, we should add support for long-based indexing.

This will also help with Clojure interop for vectorz-clj, since Clojure prefers long values rather than ints for most purposes.

Internal data formats may use either int or long values. ints will offer greater space efficiency and work better as array indices, so should be preferred unless long sizes are required.

[mikera]

This has now been completed for getXXX operations. setXXX operations outstanding