Promise examples

I'm very sorry for the delay.

For these examples I wanted to:
  * Avoid writing high level abstractions
  * Show useful examples of stuff that can be expanded into Gallery modules

That's why you'll see a cache mechanism (Luke's suggestion), a utility class for treating promises as arrays and a Y.Node plugin for chaining async operations like `transition()` or `load()`.

One question: Selleck keeps asking me for tests? Should I write them?