Dtools-datastructures

* data structures now support a much more FP style for Python
* implemented Maybe monad
* introduces the use of type annotations for this effort
* much better test coverage

* begin work on a more functional approach
* create a monadic Option class
* drop the subclassing of NONE
* put this effort on a new branch: feature_maybe
* some flaws with previous approach
* the OO redirection not best
* for a class used in computationally intense contexts
* adds way too much complexity to the design
* some Python library probably already implemented this
* without looking, these probably throw tons of exceptions
* more fun implementing it myself
* then being dissatisfied with someone else's design

* subtle paradigm shift for Stack class
* empty Stacks no longer returned for nonexistent stacks
* like the tail of an empty stack
* singleton Stack.stackNONE class object returned instead
* Stack & _StackNONE classes inherit from _StackBase
* still working out the API

* updated class Dqueue
* added __eq__ method
* added equality tests to tests/test_dqueue.py
* improved docstrings

* added __eq__ method to Stack class
* added some preliminary tests
* more tests are needed
* worst case O(n)
* will short circuit fast if possible

* decided base package should have no dependencies other than
* Python version (>=2.10 due to use of Python match statement)
* Python standard libraries
* made pytest an optional \[test\] dependency
* added src/ as a top level directory as per
* https://packaging.python.org/en/latest/tutorials/packaging-projects/
* could not do the same for tests/ if end users are to have access