refactor: migrate to use upstream GraphQL

[namit-chandwani]

An attempt to fix the issue: aerogear/graphql-link#41.
Based on discussions in PR: aerogear/graphql-link#57.

Checklist of Imports

Following is a list of imports that graphql-link uses from this fork of graphql.

I have planned to work on one package at a time and update this checklist as soon as that package is successfully converted to make use of the upstream GraphQL repo.

• "github.com/chirino/graphql"
• "github.com/chirino/graphql/schema"
• "github.com/chirino/graphql/qerrors"
• "github.com/chirino/graphql/graphiql"
• "github.com/chirino/graphql/httpgql"
• "github.com/chirino/graphql/resolvers"
• "github.com/chirino/graphql/exec"
• "github.com/chirino/graphql/customtypes" (Not directly used by graphql-link)

Further comments

The commit currently attached to this PR makes the "github.com/chirino/graphql/qerrors" package to import and use the "github.com/graph-gophers/graphql-go/errors" package of upstream repo by making some changes in the relevant files.

Once this commit change gets approved, I'll move on to work on any of the remaining packages from the checklist above, by adding further commits to this PR itself.

If there is any fault in my approach then please let me know, I would be happy to make the necessary changes according to the requirements.