* Correct whitespace issues in 6_button.py
* Make "painter" a class variable (self.painter)
* Reference `self.clear_canvas` when binding the clear button callback
* Call `self.painter.canvas.clear()` in button callback
* Adjust the number of parameters for callback method
This fixes a large number of white space errors in the examples/
directory.
When I upgraded Makefile to check the 'make style' on the examples
directory,
the output was hundreds of lines long. Currently, the output is
managable
and consists solely of "lines too long", as kv lines cannot be split.
This
commit touches an obscene number of files in trivial ways.