Make distinction of guard expressions and functions/operators (#9497)
Make distinction of guard expressions and functions/operators (#9497)

* Clarify distinction of guard expressions and functions and operators.
* Recommend using type-check guard functions.
* Reorder sections such that the "multiple guards" section immediately follows the "errors in guards" section.
kimshrier/elixir,ggcampinho/elixir,pedrosnk/elixir,michalmuskala/elixir,ggcampinho/elixir,kimshrier/elixir,kelvinst/elixir,elixir-lang/elixir,kelvinst/elixir,pedrosnk/elixir,joshprice/elixir