Hi Guix!

I figured there was a small issue with our maven package. It warns that
the current logger is not supported, and lists no supported logger.
This is because I forgot to copy resources in maven-embedder (first
patch). I also noticed I missed resources in maven-compat, so I fixed
that in the second patch.

Then, maven uses its own logger instead of a default one, even if it
does support slf4j-simple. The third patch adds maven-slf4j-wrapper. It
is essentially a fork of slf4j-simple, but the way it's written
requires me to copy most of slf4j-simple's sources. The last patch
switches the use of slf4j-simple to maven-slf4j-provider. I checked
that java-jmh still builds properly with this change, and no warnings
are shown about the logger anymore.