title: Git submodule from just a directory of another repository
body: <p>Is it possible to create a submodule that does not link to a repository directly, but to a directory inside it?</p>
  
  <p>For example, let fw.git be a framework repository, with these dirs:</p>
  
  <pre><code>|fw.git
  \---|test
      |code
      |tools
  </code></pre>
  
  <p>I'd like to submodule the framework code, just the <code>code</code> directory, not other directories.</p>