Upgrade Hiccup & fix tests

When I was trying to `lein2 marg` on a Compojure project, I got an exception about a missing function `escape-html`. In Hiccup's change to 1.0, it moved `hiccup.core/encode-html` into `hiccup.util/encode-html`, so I updated Marginalia's source accordingly.

In order to make sure upgrading Hiccup didn't break anything, I attempted to run Marginalia's tests. When those also spewed exceptions, I made a few edits to them too.