Heirarchical traits, cleanup, fixes, and improvements.

[amcgregor]

• Heirarchical base trait.
• HPath path-based heirarchical trait.
• HParent adjacency list-based heirarchical trait.

Additional substantial changes:

• Fix: Filter comparisons involving None values attempting to utilize typecasting.
• Add: Date field timezone conversion and naïve date handling.

Additionally:

• Minor optimizations for CPython.
• More and better documentation.
• Cleanup of dead imports, code, testing, deprecation warnings, and Python egg legacy.
• Updated dependencies, and preferential use of pytz.utc over bson.tz_util.utc if available.
• In the Queryable (beta) trait, await is becoming a reserved word in Python 3.7 so use wait instead.

[codecov]

Codecov Report

Merging #41 into develop will decrease coverage by 10.27%.
The diff coverage is 33.75%.

@@             Coverage Diff              @@
##           develop      #41       +/-   ##
============================================
- Coverage      100%   89.72%   -10.28%     
============================================
  Files           51       52        +1     
  Lines         1835     2053      +218     
============================================
+ Hits          1835     1842        +7     
- Misses           0      211      +211

Impacted Files	Coverage Δ
marrow/mongo/core/trait/heir/hparent.py	0% <0%> (ø)
marrow/mongo/core/trait/heir/hpath.py	0% <0%> (ø)
marrow/mongo/core/trait/heir/base.py	0% <0%> (ø)
marrow/mongo/core/trait/queryable.py	100% <100%> (ø)	⬆️
marrow/mongo/core/field/ttl.py	100% <100%> (ø)	⬆️
marrow/mongo/util/__init__.py	100% <100%> (ø)	⬆️
marrow/mongo/core/trait/identified.py	100% <100%> (ø)	⬆️
marrow/mongo/core/field/array.py	100% <100%> (ø)	⬆️
marrow/mongo/query/query.py	100% <100%> (ø)	⬆️
marrow/mongo/core/field/date.py	81.53% <79.66%> (-18.47%)	⬇️
... and 16 more

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