Add Rank overloads with OrderByDirection

[Head0nF1re]

resolves #544

Source:

• Add Rank overloads with OrderByDirection in SuperLinq and
  SuperLinqAsync. This allows the user to choose the ordering direction
  when ranking the sequence

• Add new public methods to PublicAPI.Unshipped.txt

Tests:

• Add tests based on the existing tests for Rank and DenseRank operator.
• Add a summary for some tests that didn't had one.

Docs:

• Use a simpler language to describe how the items will be ranked.
• Add parameter sortDirection in new methods.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (809a44d) 93.30% compared to head (4bf5ae5) 93.34%.
Report is 2 commits behind head on master.

Files	Patch %	Lines
Source/SuperLinq/ValueTupleEqualityComparer.cs	30.00%	6 Missing and 1 partial ⚠️
Source/SuperLinq/ScanRight.cs	87.50%	0 Missing and 1 partial ⚠️
Source/SuperLinq/Sequence.cs	88.88%	0 Missing and 1 partial ⚠️
Source/SuperLinq/ValueTupleComparer.cs	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #620      +/-   ##
==========================================
+ Coverage   93.30%   93.34%   +0.03%     
==========================================
  Files         242      248       +6     
  Lines        7767     7813      +46     
  Branches     1596     1604       +8     
==========================================
+ Hits         7247     7293      +46     
  Misses        329      329              
  Partials      191      191              

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[Head0nF1re]

Forgot about DenseRankTests, will add those tomorrow

[viceroypenguin]

couple minor fixes, and should be good to merge. thanks!