Extensible bugsnagExceptionFromSomeException

[pbrisbin]

The current function only handles exceptions known to Control.Exception, there should be an easy way to support site-specific exceptions. This may require exposing our Caster stuffs.

[pbrisbin]

I think I'm going to slim down the library, and really only expose notifyBugsnag(With), and have it take SomeException. In addition to obviating this issue, this would mean:

• BugsnagException has Exception, so throwing/catching that doesn't change
• We can put you custom [Caster] list on settings, which is a better place for it IMO
• We can remove a bunch of functions from the library API

I was writing up the main module docs for Network.Bugsnag with this approach in mind and the story reads a lot nicer, which I think is a good sign.