now works with vector<vector<X>> and array<array<X,n>,n>

Perhaps it was premature of me to call the previous release "stable". The ability to use vector<vector> instead of X** was supposed to be working in v1.0.0, but the tests I wrote in the previous commit were failing to compile the way I thought they were, causing me to erroneously believe it working. Hopefully this release really is stable.