CLI code generation: how can we support globbing?

[tomhoule]

I don't have a lot of time to elaborate right now, but other graphql code generation CLIs support passing a glob of all query files to generate code for (e.g. src/**/*.graphql) and dumping the result into one module. apollo-codegen for example supports this.

There are a few problems with this in the context of this project:

• how do we select the operation inside a query document? Do we only take the first? All of them? A custom annotation?
• It would be nice if we could also implement code sharing for fragments and enums.

[mathstuf]

Related to #102.

[tomhoule]

Also related to #134