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.
It's not an issue of cost, it's that the two formulas are different. If the variances are assumed equal, then all of the observed samples can be used to update the same variance estimate. If the variances are unequal, then there is uncertainty in both of the variances which must be factored into the estimate of the difference in the means. Two separate functions is fine with me.