More universal methods in the main package

[axefrog]

I want the main package to expose more methods that are interchageable among collections, including methods for shallow getting/setting, iteration, and for creating new collections and so forth.

• [ ] Collection-creation functions; var list = Collectable.List()
• [ ] As per #40, export a full set of (optional) exports, providing a set of namespaced functional interfaces, but with the prepackaged convenience offered by the Immutable.js approach.
• [ ] Universal methods, e.g. get() and set(), that looks at the collection type to determine which operation to perform.