Early matrix/vector support

 a reimplementation of the numpy matrix class, with:
 - slightly different printing
 - convenient element-wise functions
 - overloaded <= for constraint generation

Resolves #8.
I tend to avoid lambdas (a habit picked up from a team I worked on -- makes debugging and profiling easier). Also suggested here: https://docs.python.org/2/howto/functional.html. Any reason not to implement each of these via `def`?