Implement 1D DG Advection Example

This adds enough infrastructure to support the 1D DG example from Arrayzy.

Includes the following:

• Support for matrix products
• Support for a NumPy-like user-facing interface: matmul, roll, tranpose, stack
• __getitem__ support (in the form of very basic slices)
• Implementation of new input argument types: SizeParam, DataWrapper
• Binary arithmetic operators (bonus: unary operators)

Things that are not included:

• NumPy compatible arithmetic (#11)
• Respecting tags in code generation
• Supporting slice fully (see TODO in the code)