Make properly enumerable about ampersand-collection

[aaronmccall]

This will have to wait until ES6 lands in browsers most likely at which time proxy should allow this to be done quite easily. See http://www.nczonline.net/blog/2011/09/15/experimenting-with-ecmascript-6-proxies/ about halfway down for reference.

[wraithgar]

Should we document to use collection.models until then and also encourage renderCollection instead? The idea of passing things into your template seems incongruous w/ bindings imo.

[pgilad]

I think using collection.models to iterate (say in jade templates) is the way to go, it should be noted specifically with an example in the readme.