Add support for h(function_name) helper in IEx
Add support for h(function_name) helper in IEx

Allows printing documentation for IEx helpers and Kernel's functions/macros without specifying arity.

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