title: Continue after single failed required package Installation
body: <p>I'm trying to pip install a python package A. One of the requirements for A is package B which fails to install on Windows and thus fails the entire installation of A. </p>
  
  <p>However, A has lots of useful functionality that doesn't require B. Can I force pip to ignore errors during installation of dependencies?</p>
  
  <p>I could use --no-deps but that would mean I need to find all the other requirements of A and install them individually. </p>