Enable easier event building for context supports

[dcramer]

Right now it seems fairly complex to utilize User/Http contexts. It might make sense to do something similar to the following pattern for APIs:

event = Raven.GetEventFromError(...)
event.User = UserInterface(...)
Raven.Send(event)

(Pardon my entire lack of familiarity with C# :)

[asbjornu]

@dcramer I'm not sure, but I believe #71 covers this quite well and that the latest prerelease of develop contains improvements in this area.

[asbjornu]

Now that we have SharpRaven.Nancy out with support for capturing HTTP context information from Nancy, I feel we have an idea on how to solve this for different environments. Since HTTP context stuff usually isn't interface based, it's hard to abstract much more, at least until OWIN is the only interface we need to cater to. I'm therefore closing this.