Fix some docs in the `Atom` module
Fix some docs in the `Atom` module

- Changed a `@doc` to `@moduledoc` so that the `Atom` module has a module
  documentation
- Added examples to both `Atom.to_string/1` and `Atom.to_char_list/1`

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