`forge()` does not write the modified message to `out`

[pavel-kirienko]

The docs state that out is populated with the modified message but it is not:

https://github.com/resilar/crchack/blob/7902c0541931b352c8df838e11acc9e558a0454d/forge.h#L31

The out argument is currently unused. I might be being overly pedantic since the docs are admitted to be incorrect, but still.

Thank you for this tool, by the way, it is quite helpful!