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.
But it doesn't cover both cases. The two formulas are different. If the two variances are not assumed equal, you combine them with 
sqrt( s1^2 / n1 + s2^2 / n2)

If they are assumed to be equal, you use all of the samples to update the estimate of the standard deviation

sqrt{ [ (n1 - 1) s1^2 + (n2 - 1) s2^2 ] / (n1 + n2 - 2) ]}

These can be quite different, especially if you have a small number of samples in one of the datasets.