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.
If these are the correct arguments, then they should be listed as 
WelchT(mean1, std1, size1, mean2, std2, size2 float64) float64

However, is this particular combination going to be pretty common? Is it worth defining a datatype that is
struct {
   Mean float64
   StdDev float64
   Size float64
}