Dev/start5 (#68)

* Change to .NET Standard 2.0. Make structs readonly. Start to rip out statistics container classes. Add ChebyshevU. Add Benford and SkewNormal distributions.

* Beta use unit interval. no Sample, and other cleanup.

* Many mostly small improvements to accuracy and added tests.

* Final changes to prep for release.

Dev/working3 (#63)

* New Interval.Contains method. Documentation.

* 4.1.4 version

Merge pull request #39 from dcwuser/dev/examples

Dev/examples

Tag for 3.1 release