Dependencies as submodules

As per http://opendylan.org/documentation/getting-started-cli/adding-new-libraries.html ...

One should be able to build wiki by:

    export OPEN_DYLAN_USER_REGISTRIES=/path-to-wiki/registry
    cd /some/where && dylan-compiler build wiki

**ATTENTION**

I'm not using the latest http module, as I'm unable to compile it. (I'm using this https://github.com/dylan-lang/http/tree/9fc52a24167272aa0af68bda6462262804658315)