Add header above footnotes

[Sogolumbo]

Currently the footnotes look just like any list. To avoid confusion I think there should be the option to add a headline above the footnotes.
The content of the headline could be set by a new option (e.g. a string var FOOTNOTE_TITLE).
If the string is empty no header should be inserted. Otherwise I'd choose an h3 element.

Additionally I would add the option to insert a horizontal line hr (This could be controlled with the option FOOTNOTE_HORIZONTAL_LINE).

[Sogolumbo]

Here are some screenshots: