Support Directives

[numso]

We've already got an idea of what the syntax of these should be. And Goblet.Parser is already parsing them out. We just need to spend the time to understand how directives are defined in the schema so we can generate queries correctly as well as validate the correctness of written queries.

query "Test" do
  @include if: ^something
  someField
  @special info: "this is a custom arg"
  someOtherField
end

should be validated and then output

query Test($something: Boolean) {
  someField @include(if: $something)
  someOtherField @special(info: "this is a custom arg")
}