Dtools.fp

* fp.iterables `foldL_sc` & `foldR_sc` now have
* common paradigm
* similar signatures

* added fp.iterables function `foldR_sc`
* shortcut version of `foldR`
* not fully tested
* docstring not updated

* added fp.iterables function `foldL_sc`
* shortcut version of foldL

* removed woException `XOR` method
* `getDefaultRight(self) -> R`:
* added methods
* makeRight(self, right: R|Nada=nada) -> XOR[L, R]:
* swapRight(self, right: R) -> XOR[L, R]:

* fp.iterables no longer exports `CONCAT`, `MERGE`, `EXHAUST`
* for grscheller.datastructures
* grscheller.datastructures.ftuple
* grscheller.datastructures.split\_ends

* class Nothing re-added but renamed class Nada
* version grscheller.untyped.nothing for more strictly typed code