publication time and date and the last modified time and date
independently.
This makes it possible to access the last updated date with {{ article.locale_modified }} in templates.
Additionally, an already delivered feed entry can be corrected by changing the modified date and time, as it is used for atom:update
/ rss pubDate field now.
Markdown instance carries state for subsequent uses. Content
and summary parsing is done with the same instance. Since
footnotes are processed with an extension and stored as state,
content footnote is duplicated for summary.
This PR adds a ``.reset()`` call before summary parsing to clear
the state. It also adds a test case with footnotes.