readthedocs examples are broken again

[eharpste]

The readthedocs examples seem to be breaking in generating their images again. That usually means we introduced something that is taking too much run time. Worth looking into.

[eharpste]

Also the datasets module doesn't seem to render on readthedocs.

[eharpste]

@cmaclell recently discovered that many of these issues was due to some unicode problems. We still don't get images in all examples because they take too long.