Dtools.datastructures

* Started work on a Left biased Either Monad
* removed isEmpty method from Stack class

* Maybe get() and getOrElse() API changes
* getting a better handle on type annotation
* work-in-progress
* erroneous LSP error messages greatly reduced

* 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