added z-score function
refactored mode function to pattern match instead of using if/else
added hex.pm version number candy
added math helpers module
placeholder module and test
added placeholder functions
created the cdf function
added the cdf function (without size parameters)
nicer 'ternery-ish' expression
added location/size parameters to cdf function
added tests to the math helpers module
added random number draw from distribution
added ppf function
added ppf function
added location/scale to ppf function