Add doc about ignore: :whitespace to Base.decode64.
Add doc about ignore: :whitespace to Base.decode64.

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