If `global` is used and handlebars is compiled for browser
usage without a Node.js `global` polyfill, handlebars
fails with a `global is undefined` error.
Fixes#1593
* Added support for iterable object in {{#each}} helper
Currently {{#each}} helper supports either arrays, or objects,
however nowadays you can define custom iterable objects by overriding
a special method called Symbol.iterator, which results in empty result
being rendered.
* improved a test for iterables in {{#each}} returning empty result
* #each helper: using ES5 instead of generator functions in tests
* #each helper: using ES5 in the helper itself