code: private void addFootnoteRef(MacroMarkerBlock footnoteMacro, Block footnoteRef)
      {
          footnoteMacro.getChildren().clear();
          footnoteMacro.addChild(footnoteRef);
      }
docs: Add a footnote to the list of document footnotes. If such a list doesn't exist yet, create it and append it to
  the end of the document.
  
  @param footnoteMacro the {{footnote}} macro being processed
  @param footnoteRef the generated block corresponding to the footnote to be inserted