* Reorganizes codebase to rely on properties instead of methods.
* Adds `ForSubclassEyesOnly` category to expose protected interfaces needed by subclasses to implement notice types.
* Removes the `noticeType` notion in favor of using subclassing to create notice types.
* Removes seemingly unused `defaultManager` static method.
* Removes `_raiseIfObjectIsNil:named:` method in favor of `NSParameterAssert`
* Adds Appledoc documentation to all public interfaces.
* Adds a Boolean argument to the dismiss callback block to disambiguate interactive vs. non-interactive dismissal.
* Replaces the dimissed block property with a setter method to enable code completion in Xcode.
* Adds Default-568h@2x.png image to suppress Xcode warning.
