title: How to write a custom pooling layer module in tensor flow?
body: <p>I have thought that adding a new module which will do the center pooling. </p>
  
  <p>I was looking in the tensorflow code and there is a file named <code>gen_nn_ops.py</code> which internally calls function from another file by passing "Maxpool", "AvgPool", etc. parameters to do the required computation.</p>
  
  <p>I want to do centre pooling which selects the center element in the window. I have code ready for the matlab and c++ versions but need to know how to add a new module in TensorFlow for such computation. Also where to set the backpropogation code. </p>