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More features!
SPF can only be instantiated once per App now. If you try to create a new SPF for a given app, it will give you back the existing one.
Plugins can now be registered into SPF by using the plugin's module, and also by passing in the Class name of the plugin. Its very smart.
Plugins can use the legacy method to register themselves on an app. Like ``sample_plugin = SamplePlugin(app)`` it will work correctly.
More tests!
FLAKE8 now runs on build, and _passes_!
Misc Bug fixes.