Nightly breaks

This fixes the nightly breaks. Specifically:

- cast must take an explicit type.
- the boxxed ResponseWriter must be dereferenced to take an &mut.
- remedies the warnings for the deprecated `to_str_radix` with `fmt::radix`.
Haven't tried anything but the naive solution. I was just going for compilation. I'll check this right now though, and change it if it compiles correctly: two seconds..