Fix #3 built in types and directives

[AlwxSin]

There are https://github.com/vektah/gqlparser/blob/master/validator/prelude.go and prelude.graphql. But gqlfetch doesn't use gqlparser, so I can't use it either.
Just ignore built in completely.

closes #3

[suessflorian]

Hey @AlwxSin, so I ran into this as well and decided to push that responsibility to genqlient - Khan/genqlient#145. It will be cleaner to not have to manage what an explicit and implicit schema definition is here in this tool.

[suessflorian]

I still feel there is value in this, but perhaps we can have a flag like --implicit that continues to strip (rather than baking it in as a default).

What are your thoughts @AlwxSin?

[AlwxSin]

@suessflorian adding --implicit flag pretty easy in a straight way, we can pass this flag to all print functions.

But I think it's not clear enough. Maybe we can call it --without-builtins or even --without-builtins-types?

[suessflorian]

@AlwxSin, yeah I like --without-builtins, are you okay to continue on this here? Or did you want me to take care of this?

[AlwxSin]

@suessflorian yeah, I'll continue here, thanks

[suessflorian]

Looks cool, thanks for the hand @AlwxSin 👍