first attempt at (super-)UMD packaging

The approach is to _not_ try to auto-register in the Handlebars package, since we can't make any assumptions about where that library is located. (OK, as a shortcut we'll attempt to register in handlebars if it exists in the `Handlebars` global :smirk: )

There is one "test" (that doesn't work yet) run like this:  `node tests/helpers.js`