title: Reference requirements.txt for the install_requires kwarg in setuptools setup.py file
body: <p>I have a <code>requirements.txt</code> file that I'm using with Travis-CI.  It seems silly to duplicate the requirements in both <code>requirements.txt</code> and <code>setup.py</code>, so I was hoping to pass a file handle to the <code>install_requires</code> kwarg in <code>setuptools.setup</code>.</p>
  
  <p>Is this possible? If so, how should I go about doing it?</p>
  
  <p>Here is my <code>requirements.txt</code> file:</p>
  
  <pre><code>guessit&gt;=0.5.2
  tvdb_api&gt;=1.8.2
  hachoir-metadata&gt;=1.3.3
  hachoir-core&gt;=1.3.3
  hachoir-parser&gt;=1.3.4
  </code></pre>