IWebApi implementation

I have added an implementation to the bounces, blocks, spam reports, unsubscribes, and invalid emails portions of the web API interface.  I made each of those a separate interface broken out from the IWebApi interface.  I WebApi derives from each of those interfaces to keep a unified interface as well.

I tried to follow your current architecture as much as possible and I don't think I broke backward compatibility since all my contributions are additions.  If you approve, please publish a revised NuGet package.