Created CommonJS, ESM, and AMD outputs.

[shanewholloway]

First off, thanks for making probability-distributions package!

This pull request uses Rollup to create alternative outputs. The "main" entrypoint is equivalent to what you had published to date. The "module" entrypoint (.esm.mjs) allows packagers to selectively assemble modules by pulling only the needed functions. (See treeshaking in Rollup and WebPack.) In my case, I wanted to use only the PD.rnorm() Gaussian Normal function.

The second change replaces the use of eval() with a callback, enabling the expressed intent without the security issues involved with eval.

The unit tests all pass. Thanks for creating them! If you'd like to try before you merge, you can use npm install --save github:shanewholloway/probability-distributions