Promise.when adapter strategy
Switches adapter to a simple function reference (instead of a class reference)
Updates AsyncTokenAdapter docs
Merge branch 'adapter' of https://github.com/darscan/promise-as3 into darscan-adapter
Integrated "Promise.when() adapters" pull request.

Renamed Promise.removeAdapter() to unregisterAdapter() for consistency.
Refactored DeferredResponder to encapsulate its own Deferred.
Revised unnecessarily clever && and ternary statements.
Minor reformatting for consistency.
Edited comments / documentation.

Fixes #12