Add syntax for Cats NonEmptyList

[cb372]

Adds a refinedSize extension method that returns the size of a NonEmptyList as a positive int.

Based on this Twitter thread, at least 2 people in the world want this 😄

[codecov]

Codecov Report

Merging #539 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #539      +/-   ##
==========================================
+ Coverage   94.26%   94.27%   +<.01%     
==========================================
  Files          62       62              
  Lines         680      681       +1     
  Branches       14       14              
==========================================
+ Hits          641      642       +1     
  Misses         39       39

Impacted Files	Coverage Δ
...rc/main/scala/eu/timepit/refined/cats/syntax.scala	100% <100%> (ø)	⬆️

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[fthomas]

This is great, thanks @cb372!

We could also have the same for the other NonEmpty types in Cats and also for the standard library collections to return a NonNegInt. Maybe there are more methods where we could provide a more precise return type.