Feature Request: Recurring events extension

[symbolisch1234]

There is an extension to todo.txt using the "rec:xxx" key-value-pair, which makes a task recurrent, that is finishing it creates a new task.

i use https://github.com/mpcjanssen/simpletask-android on my mobile, where this functionality is implemented, so i have quite a number of tasks with the "rec:xxx" key-value-pair. if i mark these as done in thunderbird, i have to manually add a new task, with the same content.

please see https://github.com/mpcjanssen/simpletask-android/blob/master/app/src/main/assets/index.en.md for more information.

Thank you for considering!