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.
From what I see, the formulas are not the same depending on the assumptions (and it makes sense they wouldn't be). Are these the only two distinct cases? It seems like they would have to be, but just checking (otherwise we may want to define a constant type).

The boolean can be renamed  assumeEqual  (with the comment that it means standard deviations)