Upgrade django-debug-toolbar to v1.0.

As per title - this marks a break in how the debug-toolbar is installed.
There are 2 ways now to install this app; I've gone for the 'explicit' setup, as the 'quick setup' comes with several caveats and edge cases where it doesn't work (and I have already experienced this!).
At the same time I've changed the links in the comments: instead of pointing to the Github page, I've redirected them to readthedocs. I trust that this is ok?