This will likely be the last beta before a 2.0.0 stable version.

- Comprehensive child collection support via a number of utilities:
  - You can now set the identifier name in each ResourceController instance;
    this value will be used to both retrieve the identifier from the request, as
    well as to generate URIs.
  - HalCollection now composes the identifier name as provided to the
    ResourceController, instead of hard coding 'id' as the name.
  - Added ResourceEvent class, used by the Resource class when triggering
    events.  It encapsulates Route and Query parameters in addition to the
    resource and data passed via the controller, allowing developers to access
    these via listeners. This allows for access to things like the parent
    identifier (via route parameter), sorting and filtering information for
    collections (via query parameters), etc.
- ApiProblem additions
  - Provides default titles for all common HTTP error status codes.
  - A new interface, ProblemExceptionInterface, allows you to provide the title,
    describedBy URI, and additional details via the exception.
- New abstract factory for resource controllers, which greatly simplifies the
  process of configuring and wiring ResourceController instances.