title: Handling external libs with rebar
body: <p>I want to use some libs in my application, like <a href="https://github.com/Panmind/erlang-ruby-marshal" rel="noreferrer">https://github.com/Panmind/erlang-ruby-marshal</a>. That repo holds an src dir, but has no .app file (because it's not an application), so I can't use get-deps.</p>
  
  <p>I tried another approach, adding a <strong>libs</strong> dir in sub_dirs and added the repo as a git submodule, but rebar won't compile any of its files. I guess that rebar only compiles otp applications, but not just .erl files that aren't tied to an application.</p>
  
  <p>How do you manage those kind of dependencies? I would like to avoid copying the files to my app dir, because I don't think they belong there, and I kind of like the git submodule approach, that allows me to keep track of the lib version I am using.</p>