[GSoC 2018] Add Markdown editing in iOS app

We would like to extend the ability to edit plain text files to Markdown files (ending .md, .markdown, …)
It would enable the same functionality to edit these files like the .txt files. The project can be led further if a student wants to work on that, like adding Markdown functionalities. More information here.

Feel free to ask for help if you want to get started!