Allow respond_to to be overridable.
Allow respond_to to be overridable.

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