Scan: ICollection<> implementation

[viceroypenguin]

This PR adds an ICollection<> implementation of the Scan operator.

Fixes #384

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03 🎉

Comparison is base (0cd4e5a) 87.43% compared to head (f052899) 87.47%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #385      +/-   ##
==========================================
+ Coverage   87.43%   87.47%   +0.03%     
==========================================
  Files         239      239              
  Lines        7189     7207      +18     
  Branches     1675     1677       +2     
==========================================
+ Hits         6286     6304      +18     
  Misses        462      462              
  Partials      441      441              

Impacted Files	Coverage Δ
Source/SuperLinq/Scan.cs	100.00% <100.00%> (ø)

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