Add discret distribution (bernoulli, geometric, poisson, binomial)

Add mode tests on distribution

Make `Float80` extension only available to OS X

Carthage would fail to compile on iOS, watchOS, and tvOS.

Go back to using umbrella header over module

Prepare 1.4.0 release

Update README.md with latest info

Prepare 1.2.0 release

Prepare 1.1.0 release

Fix Double and Float random generation