Added support for raw input endpoints

This add a setting called `raw_input`.

It disable the parsing of the request and let this responsibility to the developer.

It also covers support for wildcard incoming content type. I thought some time about this, and I think it would be a lot of refactor for a feature that has not real meaning without "disabling" the parsing of the input. That's why `raw_input` also bypass the check of the incoming content type and let the developer do that too.

I added an example to the README explaining the use of this option.