Add exampleTransform.py from the master branch, modified to work on 1.16

I found the exampleTransform example in the master branch quite useful. However as 1.16 is still very much in use, I backported the example to work on 1.16.

As editing of mapped buffers is not easily achievable (as far as I know) on versions below 1.17. I modified the example to copy the buffer content for editing, then copy it back to the buffer.