Add option to copy only part of the code

[polyrand]

This would be useful to add examples inside the code snippet, for example:

"""tag1 array flatten tag2 numpy tag3""" 

import numpy as np

matrix = np.array([[1, 2, 3],
                               [4, 5, 6],
                               [7, 8, 9]])
#pasteon
matrix.flatten()  # array([1, 2, 3, 4, 5, 6, 7, 8, 9])
#pasteoff

When ctrl-p (or any key is finally chosen) is pressed, only the code between #pasteon and #pasteoff will be copied to clipboard, that way you can have an example inside the snippet but without having it copied to the clipboard.