Adding initial information theory functions

[galengorski]

These are initial information theory functions, the major functions:

• calcMI, which calculates the mutual information between two variables
• calcMI_crit, which calculates the "critical MI value", a way of assessing the significance of MI values. This is done by calculating the MI from randomly shuffled data some number of times and setting a threshold.

[galengorski]

Thanks for the review @jds485 , I'll add these changes in. Next steps are TE, and U,R,S formulations