* MAINT: Move `Fracdiff`, `FracdiffStat` to sklearn/ (close60)
* Importing them as `from fracdiff.Fracdiff`/`from fracdiff.FracdiffStat` is deprecated. Instead, please import them as `from fracdiff.sklearn import Fracdiff`/`from fracdiff.sklearn. FracdiffStat`.
* CHORE: Add Typecheck (73)
* CHORE: Update Makefile, CI, and Building documentation (71) (72) (74)