<p>Some modules might not be not part of the riot tree (oonf_api, <a href="https://github.com/benpicco/riot-libs">riot-libs</a>).<br>
Add a way to include them into the Make process. </p>

<hr>

<h4>You can merge this Pull Request by running</h4>
<pre>  git pull https://github.com/benpicco/RIOT external_modules</pre>
<p>Or view, comment on, or merge it at:</p>
<p>  <a href='https://github.com/RIOT-OS/RIOT/pull/75'>https://github.com/RIOT-OS/RIOT/pull/75</a></p>

<h4>Commit Summary</h4>
<ul>
  <li>allow external modules to be added to a project</li>
</ul>

<h4>File Changes</h4>
<ul>
  <li>
    <strong>M</strong>
    <a href="https://github.com/RIOT-OS/RIOT/pull/75/files#diff-0">Makefile.include</a>
    (2)
  </li>
</ul>

<h4>Patch Links:</h4>
<ul>
  <li><a href='https://github.com/RIOT-OS/RIOT/pull/75.patch'>https://github.com/RIOT-OS/RIOT/pull/75.patch</a></li>
  <li><a href='https://github.com/RIOT-OS/RIOT/pull/75.diff'>https://github.com/RIOT-OS/RIOT/pull/75.diff</a></li>
</ul>