def context(description, context_class = Riot::Context, &definition)
    Riot.context(description, context_class, &definition)
  end
Defining +context+ in Object itself lets us define a root +context+ in any file. Any +context+ defined
within a +context+ is already handled by {Riot::Context#context}.

@param (see Riot.context)
@return (see Riot.context)