Build CommonJS versions of packages, add Node test runner

Oh my, what fun.

Depends on the trivial https://github.com/tildeio/simple-html-tokenizer/pull/11

* This adds CJS build output from ES6.
* It also inlines dependencies for distribution. Handlebars and simple-html-tokenizer are both inlined to the appropriate AMD packages.
* It introduces a test runner for Node. For now, tests are whitelisted into node. First flag the package with `node: true` in `packages/index.js`, then be sure the file ends with `-node-test.js`.
* Adds an `htmlbars` package that includes both the compiler and the runtime.

Mostly I'd like to see a :+1: from @rwjblue, but anyone else please take a look as well. From here we can refactor the compiler tests to run in Node, as they should before we start thinking about pre-compilation.
Is this variable used?