use highlighted word as footnote marker

[katrinleinweber]

This is connected to #306. Again, for long documents, esp. when split into several files and processed further with Pandoc, the default way of inserting footnotes as [^1], [^2], etc. can cause duplicates. How about (adding an option to) using the currently highlighted word.

Example: Chemical XYZ[^XYZ] is suspected of causing something.

[felixhao28]

This feature will be added when v2.1.5 comes out. Thanks for suggestion.

[katrinleinweber]

Thank you for implementing it :-)