FSRS

[migueltorrescosta]

Is your feature request related to a problem? Please describe.
FSRS outperforms SM-2 in memory retention, having been adopted by Anki and other similar tools.

Describe the solution you'd like
Replace SM-2 with FSRS

Describe alternatives you've considered
Forking the repo to implement FSRS

Additional context
The algorithm used reduces annoyance with revisiting cards unnecessarily

[DavidMiserak]

Thanks for bringing this to my attention. It may be a good idea to support multiple Spaced Repetition algorithms that a user could select.

[DavidMiserak]

Please checkout the develop branch and try to manually test the FSRS.