A start to the Sphinx doc, a bug fix, some new features

Biggest changes:

- A Sphinx doc tutorial draft.
- Added 'scidbname' argument to new_array to bind to existing SciDB arrays
- Fixed (tiny) load query bug affecting multi-instance SciDB clusters (I don't support parallel load from the shim)
- Reised matrix multiplication to support arrays with varying schema and to use GEMM when possible