Updates to support publishing to npm

[bikegriffith]

Fixes #1

Adds UMD module definition wrapper so it can work with a require or import module workflow, while retaining ability to be directly included as a <script> in a browser.

NOTE -- I did not actually publish this to npm, but I could easily if you want. I did test locally with a separate project via npm install ../path/to/timetable.js/ (verified in both a headless node and browser environment). I thought it might make sense for it to stay in your @Grible namespace in npm.

Steps to complete publishing:

npm run build
npm login
npm publish