add empty line before the footnote definition

[chrisgrieser]

when there is no empty line at the end of the text, the plugin will add the footnote text directly below the text – however, having a line break in between those would be cleaner to read.

[wjfeeney]

This plugin needs to insert an empty line space after insertion of the footnote number. If not, the footnote(s) is not rendered properly. Top image=no space; bottom image=empty line space between.