Some backward compatibility breaking changes:

[marchant]

- Native Maps, WeakMaps and Sets are now used when available
- Aligns Map with latest standard with PR #137
    - Use of a second argument for default value in get() is deprecated
    - keys(), values() and entries() now return an iterator per standards,
      methods returning an array are now keysArray(), valuesArray(), entriesArray()
    - It's not possible to create a Map by passing an anonymous object to the constructor, that feature is now available as Map.from();

• Introduces .from() method on constructors.
• Fixes circular dependencies by isolating core map/set/list features in their own package-private file