Refactoring + custom errorClass + attempt to address #1, #3

[taoeffect]

• Proper scoping, avoid polluting global namespace with functions
• Improved/corrected UMD support
• Added custom errorClass support
• Inlined a function that was only called once
• Partially (or completely) addresses issues #1 and #3

[taoeffect]

Note that because I ended up going with a (slightly modified) version of vue-form, I did not test these changes!

[acstll]

I've tested this locally and it looks good to go! I'll merge and cut a minor release with it.

One last question: were the JSDoc comments useful to you or did they feel like clutter?