title: getting the row and column numbers from coordinate value in openpyxl
body: <p>I'm trying to covert a coordinate value in excel to a row number and column number in openpyxl.</p>
  
  <p>For example if my cell coordinate is D4 I want to find the corresponding row and column numbers to use for future operations, in the case row = 3, column = 3. I can get the row number easily using  <code>ws.cell('D4').row</code> which returns <code>4</code> then it's just a matter of subtracting 1. But a similar argument <code>ws.cell('D4').column</code> returns <code>D</code> and I don't know how to easily get this into int form for subsequent operations. So I turn to you wise folks of stackoverflow. Can you help me?</p>