We show how to change namespace by creating a new context, then
switching to the new context. It works, but it is very cumbersome.
Instead, let's just update the current context, and give some
details about when it's better to update the current context, and
when it is better to use different contexts and hop between them.
This was discussed and agreed in #246. It will probably break a few
outstanding PRs as well as a few external links but it's for the
better good long term.