Expose exceptions happened during TdLib.Bindings.Receiver::ProcessEvents

[ForNeVeR]

While discussing #167, we've found that there's an event TdLib.Bindings.Receiver::ExceptionThrown that is emitted when there's an error during the loop in TdLib.Bindings.Receiver::ProcessEvents.

But this event is never exposed to the user; it's impossible to know there even was an error, since the receiver type is internal.

We should think about exposing it somehow: at least in the form of a user-visible event.