Dtools.fp

* forgot to update README.md on last PyPI release
* simplified README.md to help alleviate this mistake in the future

* from last PyPI release
* added accumulate function to fp.iterators
* new fp.nothing module implementing nothing: Nothing singleton
* represents a missing value
* better "bottom" type than either None or ()
* renamed fp.wo_exception to fp.woException
* overall much better docstrings

* replicated functionality from grscheller.datastructures
* grscheller.datastructures.fp.MB -> grscheller.fp.wo\_exception.MB
* grscheller.datastructures.fp.XOR -> grscheller.fp.wo\_exception.XOR
* grscheller.core.iterlib -> grscheller.fp.iterators