Improve System module type specifications coverage
Improve System module type specifications coverage

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