Add guardian (#790)
Add guardian (#790)

* Initial Guardian basic

* Apply some changes to Guardian lesson

* Move guardian lesson to libraries section

nscyclone/elixir-school,nscyclone/elixir-school,nscyclone/elixir-school,psantos10/elixir-school,doomspork/elixir-school,yuriibodarev/elixir-school,yuriibodarev/elixir-school,erickgnavar/elixir-school,erickgnavar/elixir-school,ElixirVietnam/elixir-school,doomspork/elixir-school,ElixirVietnam/elixir-school,doomspork/elixir_school,huydx/elixir-school,huydx/elixir-school,nscyclone/elixir-school,ElixirVietnam/elixir-school,psantos10/elixir-school,erickgnavar/elixir-school,doomspork/elixir_school,yuriibodarev/elixir-school,huydx/elixir-school,doomspork/elixir_school,psantos10/elixir-school,doomspork/elixir-school