Students T-Test

Added functions for Students T-Test one sample and independant sets and a function to convert a t-value to a p-value. Not sure about the naming, if you would like me to change the function names and resubmit requrest, let me know. I have tests, I will add examples next week and I would like to add dependant sets after that.
@kortschak , how do you feel about including the t-tests and P-values? My thought had been that statistical tests themselves (i.e. functions that return a probability rather than some metric) should go in their own package. The assumptions about the data are much stronger, for one.