Typespecs changes (#5875)
Typespecs changes (#5875)

* Be more explicit when describing typespecs

* Add UserDefined types and rename section in Typespecs page

Additionally reduce a Heading level

elixir-lang/elixir,kelvinst/elixir,lexmag/elixir,kelvinst/elixir,ggcampinho/elixir,lexmag/elixir,kimshrier/elixir,michalmuskala/elixir,ggcampinho/elixir,pedrosnk/elixir,kimshrier/elixir,beedub/elixir,antipax/elixir,gfvcastro/elixir,pedrosnk/elixir,beedub/elixir,antipax/elixir,gfvcastro/elixir,joshprice/elixir