Add syntax for ApplicativeError.fromEither

[tpolecat]

This adds syntax for ApplicativeError.fromEither as discussed on gitter.

[kailuowang]

👍

[codecov-io]

Codecov Report

Merging #1933 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1933      +/-   ##
==========================================
+ Coverage   95.55%   95.55%   +<.01%     
==========================================
  Files         248      248              
  Lines        4430     4431       +1     
  Branches      116      116              
==========================================
+ Hits         4233     4234       +1     
  Misses        197      197

Impacted Files	Coverage Δ
core/src/main/scala/cats/syntax/either.scala	99.13% <100%> (ø)	⬆️

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[johnynek]

nit: I would probably have rather this been pureOrRaise since the Or is usually used in to represent the failure case (at least thinking of Option[T]).