v0.9.0

Improvements

• Remove deprecated usage of Behaviour and defcallback
• Provides better support for configuring request_opts that will be used on
  every request. This is useful for configuring SSL options, etc.
• Provides support for hackneys streaming of responses.
• Better warnings when a serializer isn't properly configured.

Backward Incompatible Changes

• Responses with status codes between 400..599 will now return {:error, %OAuth2.Response{}} instead of {:ok, %OAuth2.Response{}}
• When using the ! versions of functions, {:error, %OAuth2.Response{}} will
  be converted to an %OAuth2.Error{} and raised.

Diff: v0.8.3...v0.9.0