Support extensibility for action invoker

[rynowak]

Implemented by #862

This allows you to subclass FilterActionInvoker and implement custom action invoker logic which reusing the filter pipeline. See aspnet/Entropy#23 for an example.

Fixed by 3770906

[davidfowl]

This issue has no tags and the issue you pointed to has no milestone, when was it done?

[rynowak]

this was done alpha 4 like it says?