Idris development results in a lot of transient popup buffers, which
the layer currently doesn't handle particularly well. This commit uses
popwin so that these special buffers appear in a predictable location
and opens them in motion state so that they can be closed immediately by
pressing ~q~.
These changes are largely based on the Clojure layer, which has worked
very well in my experience.
The idris-mode package has been updated to no longer use the
idris-packages variable, which allows the Idris layer to safely be
renamed to the standard for other languages.
