Prefix all Cats instances with cats, add Alternative instance for partial.Result and PartialTransformer, change instances name to something which won't change as often

[MateuszKubuszok]

TODO:

• add tests for partial.Result.orElse
• create Scaladoc for orElse
• update mkdocs for Cats instances
• perhaps use arrow name instead of category in cats.arrow instances names

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.05%. Comparing base (9c0fc38) to head (1e2a963).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #465      +/-   ##
==========================================
+ Coverage   85.77%   90.05%   +4.28%     
==========================================
  Files         124      124              
  Lines        5342     4576     -766     
  Branches      213      387     +174     
==========================================
- Hits         4582     4121     -461     
+ Misses        760      455     -305     

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