Add simple message hook

[fooker]

This hook just reads the message to send from the HTTP body which makes it easy to use this as an replacement for irker.

The channel to send to can be selected by the channel query parameter.

[fleaz]

Maybe add a small section for the new module to the README.md? (Especially the part that this can be used t replace irker would be great i think)

Rest looks good. Thanks :)

[fooker]

README.md updated with short introduction for new module.

[fleaz]

Thanks :)