Add `secotrec-aws-node` (optionally built)

[smondet]

Now that ppx_deriving_cmdliner is free, I can push this.

I leave it optionally compiled because the pinning involved; we need the master branch of ocaml-aws.

What I do looks like:

pin_all () {
    local tmpdir=$HOME/tmp/
    rm -fr $tmpdir/ocaml-aws
    cd $tmpdir
    git clone https://github.com/inhabitedtype/ocaml-aws.git
    cd ocaml-aws
    # git checkout -t origin/fix-pack-names
    opam pin add -n aws .
    for lib in $(ls -d libraries/*) ; do
        echo "Do $lib"
        opam pin add -n aws-$(basename $lib) ./$lib/
    done;
}
installs () {
    local all="aws aws-ec2 aws-sdb"
    opam remove $all
    opam install $all
}

[ihodes]

LGTM!