Add GraphiQL support

[cloudlena]

I took the template from https://github.com/graphql/express-graphql/blob/master/src/renderGraphiQL.js and go-ified it.

@sogko and others: Please let me know what you think.

If you like it, I'll add the necessary tests and make the code cleaner.

I've had some trouble adding ResultString and VariablesString. I would be glad about some advice about where to get them.

[coveralls]

Coverage decreased (-15.06%) to 79.389% when pulling 17cb4b0 on mastertinner:feature/graphiql into fab5288 on graphql-go:master.

[coveralls]

Coverage decreased (-17.4%) to 77.037% when pulling 5bc47c0 on mastertinner:feature/graphiql into fab5288 on graphql-go:master.

[coveralls]

Coverage decreased (-17.4%) to 77.037% when pulling e9334dc on mastertinner:feature/graphiql into fab5288 on graphql-go:master.

[yookoala]

This seems nice. Please do merge.

[coveralls]

Coverage decreased (-23.4%) to 71.141% when pulling 24733ec on mastertinner:feature/graphiql into 43051ba on graphql-go:master.

[coveralls]

Coverage decreased (-5.7%) to 88.889% when pulling 70ee617 on mastertinner:feature/graphiql into 43051ba on graphql-go:master.

[coveralls]

Coverage decreased (-7.4%) to 87.179% when pulling ce8e677 on mastertinner:feature/graphiql into 43051ba on graphql-go:master.

[coveralls]

Coverage decreased (-7.3%) to 87.261% when pulling e2a07d5 on mastertinner:feature/graphiql into 43051ba on graphql-go:master.

[cloudlena]

I resolved the problems mentioned above and added tests so I think this can be merged now.

[cloudlena]

@sogko, can you please comment or merge?

[yookoala]

Added comment here. No respond yet.

[ulm0]

where can the ui be reached? i'm going to /graphiql but i get a 404. thanks in advance

[cloudlena]

@klud1, it's at the same URL where your graphql endpoint is. If you reach it with a browser, it will return the GraphiQL GUI.

[ulm0]

Alright, it's working! Thanks, awesome work! Hope this gets merged asap so i don't have to tweak my build process in order to get these changes.

[chris-ramon]

LGTM 👍 — this is really awesome, thanks a lot @mastertinner! 🚢

[cloudlena]

Thanks for merging, @chris-ramon! Could you create a new release 0.2.0 which contains GraphiQL?

[chris-ramon]

Thanks for merging, @chris-ramon! Could you create a new release 0.2.0 which contains GraphiQL?

Sure thing!, https://github.com/graphql-go/handler/releases/tag/v0.2.0

[cloudlena]

Nice! Thanks, @chris-ramon!