Changes

* epub and/or PDF export of a complete issue

* Include "cite as" text on each page, with several major citation formats filled in with our data. Especially important because we use an "article number", rather than a page number -- which is supported by most citation formats, but it's not obvious from looking at an article what it's "article number" _is_, you have to know to get it from the URL. Makes it hard to cite correctly.