Error handling and logging improvements via re-raising

[grzuy]

Potential alternative to #398 .

Proof of concept still.

Haven't yet tested how compatible is with earlier elixir/otp versions.

This moves to do something "similar" to what plug_cowboy does in https://github.com/elixir-plug/plug_cowboy/blob/ced253f035f2a07ebed17cfacb64d4f16357a750/lib/plug/cowboy/handler.ex#L21-L23.