WIP: benchmarks & fix things

Perfs:

- prefer brand check of internal Constructors then an very costly instance of
  - Mixin
  - ComputedProperty
  - Alias
  - Descriptor

Mixin:
- initialization now interactions with arguments in an efficient manner
- initialization now uses a fast for loop instead of a map
- ensure the object shape stays the same (always has a mixins property)

Micro benchmarks:
http://jsperf.com/brand-verse-isntance-of