Optimize flat_map, closes #5082
Optimize flat_map, closes #5082

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