Simplifying mexfunctions

I wrote a class to be included in the mexfunction file to make processing of mexfunction simpler.

To avoid code repetition in mexfunctions you can use this class to convert from the mxArray array passed into mexFunction to c++ native data types. Each method implemented so far checks that the mxArray has the desired type and size and exists. I plan on adding new types as they crop up in our code development, though this initial class could easily be useful if you intend to code more than one mexfunction.