Filter date bounds inclusive

[benjaminotter]

Description of proposed changes

Changes filter to include the specified dates when filtering with --min-date and --max-date flags. With this change the max date filter now includes records up to and including the latest date, and likewise the min date filter also includes the lower bound.
Records with ambiguous dates such as 2020-03-XX or 2020-XX-01 are included if max date or min date lies in the same month (e.g. 2020-03-26) or year (e.g. 2020-01-23) respectively.

Related issue(s)

Fixes #683

Testing

Doctests are added for the expected behaviour.

[codecov]

Codecov Report

Merging #708 (8d7e2df) into master (5c12fd8) will increase coverage by 0.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #708      +/-   ##
==========================================
+ Coverage   30.89%   31.23%   +0.33%     
==========================================
  Files          41       41              
  Lines        5648     5715      +67     
  Branches     1365     1392      +27     
==========================================
+ Hits         1745     1785      +40     
- Misses       3828     3855      +27     
  Partials       75       75              

Impacted Files	Coverage Δ
augur/filter.py	49.24% <100.00%> (+3.26%)	⬆️
augur/distance.py	33.16% <0.00%> (-4.15%)	⬇️
augur/utils.py	40.78% <0.00%> (+3.02%)	⬆️

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[huddlej]

Very nice. Thank you, @benjaminotter!