Add a ResponseException type that can be converted to a Response

This would provide a way to allow failures to have a default representation that the backend can render if the service doesn't handle it. This will work well for things like decoders where the user doesn't typically want to deal with a parsing exception, but the client should be notified that there was a problem related to it.
A second evolution. I think I like it better.
More refinements of ReplyException
Remove TypesafeConfig dependency. #70
Merge branch 'release-0.4' of https://github.com/http4s/http4s into release-0.4
Merge branch 'release-0.4' of https://github.com/http4s/http4s into release-0.4
Make xml parsing exception message more descriptive

Add some scaladocs too.
fix scaladoc. Thanks @before.
Deal with blaze renames
Remove some dead code
Merge branch 'release-0.4'

Conflicts:
	project/Http4sBuild.scala
	servlet/src/main/scala/org/http4s/servlet/Http4sServlet.scala