Dtools-datastructures

* API breaking changes
* did not find everything returning self upon mutation
* Efforts for future directions
* decided to use pdoc3 over sphinx to generate API documentation
* need to resolve tension of package being Pythonic and Functional

* moved pytest test suite to root of the repo
* src/grscheller/datastructures/tests -> tests/
* seems to be the canonical location of a test suite
* instructions to run test suite in tests/__init__.py

* More mature
* More Pythonic
* Major API changes
* Still tagging it an Alpha release

* Queue & Dqueue no longer return Maybe objects
* Neither store None as a value
* Now safe to return None for non-existent values
* like popping or peaking from an empty queue or dqueue

* added Queue data structure representing a FIFO queue
* renamed two Dqueue methods
* headR -> peakLastIn
* headL -> peakNextOut
* went ahead and removed Stack head method
* fair since I still labeling releases as alpha releases
* the API is still a work in progress
* updated README.md
* foreshadowing making a distinction between
* objects "sharing" their data -> FP methods return copies
* objects "contain" their data -> FP methods mutate object
* added info on class Queue

* deprecated Stack head() method
* replaced with peak() method
* renamed core module to iterlib module
* library just contained functions for manipulating iterators
* TODO: use mergeIters as a guide for an iterator "zip" function
* class Stack better in alignment with:
* Python lists
* more natural for Stack to iterate backwards starting from head
* removed Stack's __getitem__ method
* both pop and push/append from end
* Dqueue which wraps a Circle instance
* also Dqueue does not have a __getitem__ method
* Circle which implements a circular array with a Python List
* Stack now implements map, flatMap, mergeMap methods
* each returns a new Stack instance, with new nodes