title: using a custom build with pbr
body: <p>I am trying to use <a href="https://pypi.python.org/pypi/pbr" rel="nofollow noreferrer">pbr</a> for a python package that has an extension module that uses <a href="https://github.com/pybind/pybind11" rel="nofollow noreferrer">pybind11</a>. There is a <a href="https://github.com/pybind/cmake_example/" rel="nofollow noreferrer">pybind11 cmake example repo</a> showing how to use cmake to build an extension module from <a href="https://github.com/pybind/cmake_example/blob/master/setup.py" rel="nofollow noreferrer">setup.py</a>. My question is: How can I incorporate this custom extension module build into a pbr-based setup.py setup.cfg? In particular, how do I use the custom extension classes, CMakeBuild and CMakeExtension, from setup.cfg? </p>