title: Saving openpyxl file via text and filestream
body: <p>I'm building OpenPyXL into an application that expects a string containing the content of the excel file, for it to write via file stream.</p>
  
  <p>From my investigation into the OpenPyXL source code, it doesn't look like it supports this kind of output. Does anyone have any experience with modifying openpyxl to support this?</p>
  
  <p>Or any general advice/workarounds?</p>
  
  <p>Thanks.</p>