Add UMD tests.

[ryan-roemer]

Fixes #9

• Add RequireJS tests
• Add Webpack tests
• Add Karma drivers for each
• Add lint for new tests
• Update documentation
• Add code coverage and travis / coveralls support.

/cc @exogen @baer @aisapatino

[baer]

Testing JS is so complicated! This looks great - :ship:

[exogen]

LGTM :+1: