Include Feature

Requirements

The user can include page title, abstract or the whole content in a given page. Headings and enumerations can be indented by a given include-level.

Which include syntax should be used?
- page include can be definde alongsite of image includes - sth. like
  &[:indent-heading s/Num :indent-list s/Num](relative or absolute url s/Str)
Which kind of urls should we accept for page includes?
- relative local urls (we will need some care to prohibit directory traversal ...)
- absolute github / gitlab / gitblit urls without authentication.
Which metadata can be used for title / abstract ?
- MultiMarcdown-Metadata is supported by clj-markdown :-)
How can we test page includes?
- we will need a content resolver component for testing and at least one for production resolving.