Tutorial 5: Advanced functions, operators, and typeclasses - init (#8)

* Init advanced functions and intro to typeclasses

Init 5th tutorial by merging 5+6 from the FPCourse

* Fixity and own operators

* Map, filter, fold intro

* Finished folds

* Info about polymorphism in Haskell

* Typeclasses, other langs, hw link

* Grammar and typos fix with Grammarly

* Improved basic typeclasses

* revisions

* Fix typos and md bugs

Author: MarekSuchanek