Fixes a number of issues in the demos.

I went through all of the demos trying to get them to run, and fixed a few things along the way.  Let me know if you'd rather have these separated out into different commits -- it was just easier to commit everything at the end.

1) Updates some imports that were no longer working

2) Uses glutInitWindowSize rather than glutResizeWindow.  glutResizeWindow is not guaranteed to size the window to the requested size, but it still calls on_resize with the requested size rather than the actual size of the window.  This means that any mouse callbacks will be incorrect, since the viewport size and the window size do not match.

3) For many of the demos, the drawing will dynamically resize to fill the window.  I feel that running thousands of things full screen is just inherently more impressive than doing it in a small window...  YMMV

4) Change window titles in some cases to describe what interactive things can be done with the demo.