Add player slug to player box score and player season totals

[jaebradley]

As #74 pointed out, player box scores and player season totals do not have a unique identifier.

The data-append-csv attribute on a player's name cell should be used - this value is the URI slug for a player's Basketball Reference Page.

[codecov]

Codecov Report

Merging #75 into v4 will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##              v4     #75   +/-   ##
=====================================
  Coverage   92.5%   92.5%           
=====================================
  Files         12      12           
  Lines        307     307           
  Branches      38      38           
=====================================
  Hits         284     284           
  Misses        19      19           
  Partials       4       4

Impacted Files	Coverage Δ
...eference_web_scraper/parsers/box_scores/players.py	100% <ø> (ø)	⬆️
...rence_web_scraper/parsers/players_season_totals.py	100% <ø> (ø)	⬆️

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[codecov]

Codecov Report

Merging #75 into v4 will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##              v4     #75   +/-   ##
=====================================
  Coverage   92.5%   92.5%           
=====================================
  Files         12      12           
  Lines        307     307           
  Branches      38      38           
=====================================
  Hits         284     284           
  Misses        19      19           
  Partials       4       4

Impacted Files	Coverage Δ
basketball_reference_web_scraper/output.py	76.59% <ø> (ø)	⬆️
setup.py	0% <ø> (ø)	⬆️
...eference_web_scraper/parsers/box_scores/players.py	100% <ø> (ø)	⬆️
...rence_web_scraper/parsers/players_season_totals.py	100% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a0bc06c...d3d9b08. Read the comment docs.