Initial setup for core functionality

Here how I was imagining the general setup and what the core components (for a standalone, Dojo, jQueyr, Mootools, YUI and Zepto version) could contain for a start:

- `extend(object, other...)`
- `isArray(collection)`
- `isEmpty(obj)` *alias: isEmptyObject*
- `isPlainObject(obj)`
- `isFunction(fn)`
- `toArray(array)` *alias: makeArray*
- `bind(fn, context)` *alias: proxy*
- `keys(object)`
- `values(object)`
- `each(collection, iterator , context)` *alias: forEach*
- `map(collection, iterator, context)`
- `filter(collection, iterator, context)`

The tests are mostly taken from the Underscore and jQuery tests. The standalone and fallback implementations are provided by [Mout](http://moutjs.com/).

[Go directly to the core branch](https://github.com/bitovi/universal.js/tree/core)

@heff and anybody else, thoughts?