Built in types and directives

[Alwx]

At this moment gqlfetch prints all types and directives fetched from a server. Problem is that build in types and directives are also printed which conflicts with genclient when I tried to generate code with error like

invalid schema file ./schema.graphql: Cannot redeclare type Float.

[Florian Suess]

This is definitely up to the consumer - I've worked with genqlient to get this sorted: Khan/genqlient#145