Support validation against multiple schemas.

[rwe]

This is a backwards-compatible change which supports multiple option groups being passed in. Tags must be unique and can refer to different schemas.

This is useful for codebases that interact with multiple GraphQL endpoints. In our case, we have multiple backend services exposing their own GraphQL schemas, and this allows us to lint their usage via backend-specific tags.

For example:

const FooQuery = Foo.gql`{ foos(first: 10) { id } }`;
const BarQuery = Bar.gql`{ bars(last: 10) { name } }`;

via the configuration:

module.exports = {
  "parser": "babel-eslint",
  "rules": {
    "graphql/template-strings": ['error', {
      env: 'apollo',
      tagName: 'Foo.gql',
      schemaJson: require('./foo-schema.json')
    }, {
      env: 'relay',
      tagName: 'Bar.gql',
      schemaJson: require('./bar-schema.json')
    }]
  },
  plugins: [
    'graphql'
  ]
}

If #26 and #28 can be merged in first, I'd be happy to rebase this against those changes.

[jackyzhen]

I have this exact use case. Please merge!

[stubailo]

Hi, sorry for the long delay - I was on vacation! If you could rebase over the other PRs then I can merge. Looks like a good change!

[rwe]

@stubailo - No worries, vacation is a good thing! Hope it was great. This has been rebased against master.

[stubailo]

Out in 0.4.0, thanks a bunch!