Updated Enthought links.

This PR updates some of the links to Enthought webpages.

It includes a typo fix, and adjustments to download links to reference Enthought Canopy instead of EPD.
In particular, it includes all of the changes which I suggested in:
https://github.com/ipython/ipython/issues/5899
https://github.com/ipython/ipython-website/pull/53