Jeff wrote this nice helper function for wrapping text to a number of pixels instead of characters.

This PR adds that function as well as an example that illustrates it's usage.

One quirk worth consideration is that the new wrap_by_pixels function returns a string with newlines inserted. Whereas the older wrap_by_characters function returns a list of the lines, and joining with the newline is left up to the code using it. I think I like the way this one does it better with the string. But the other one came from the PyPortal libraries originally, perhaps there is something in them that is using the list. Maybe it would be worthwhile to add a parameter to both that controls this behavior?