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
moved all the functions from the Statistics.Descriptive module into Statistics module; Descriptive module removed
added random number draw from distribution
added ppf function
added ppf function
added location/scale to ppf function
moved all the functions from the Statistics.Descriptive module into Statistics module; Descriptive module removed
updated readme
fixed random number generation
added docs url to readme
Merge branch 'v0.2' of github.com:msharp/elixir-statistics into v0.2
enable less-precise tests to mitigate rounding errors
extra rounding test case