Made the 1d colormap contiguous. This makes the warning go away.

Also updated to use gloo functions according to other demos.
flake8
Merge pull request #276 from per42/fix/discont

Made the 1d colormap contiguous. This makes the warning go away.
Screenshot example

Class that attaches itself to a canvas and stores the first frame. It then
saves the frame as an image file. Works on Windows since recent upstream
fix.
Updated to use on_draw
Inverted image.

Discovered and fixed that the screenshot images became upside down with
master merge.