title: Pip build option to use multicore
body: <p>I found that pip only use single core when it compiles packages. Since some python packages takes some time to build using pip, I'd like to utilize multicore on the machine. When using Makefile, I can do that like following command:</p>
  
  <pre><code>make -j4
  </code></pre>
  
  <p>How can I achieve same thing for pip?</p>