feature: show POST example how all apps do it

[maapteh]

I decided it would be nice to have an example with POST. Since it's more common. I also updated the playground which offers more options. So:

• have the TODO app working with complete working UPDATED playground which also has autocomplete (ctrl+space) on everything possible
• have app working in POST mode, with GET you show all given arguments which is not good to do on server level (security)

closes #420

credits to @atombender who showed an example :)

[coveralls]

Coverage remained the same at 92.426% when pulling 102e6e1 on maapteh:chore/example-with-post into d6b7434 on graphql-go:master.

[chris-ramon]

@maapteh thanks a lot for working on this PR 👍 –– very interesting improvement for the examples/todo.

I think GraphQL Playground is very useful tool, but I think the examples/todo aims to demonstrate how to use graphql-go/graphql as a HTTP endpoint & how to integrate it with a Web App.

But I definitely understand your motivation to improve the examples/todo to show how to use graphql-go/graphql via HTTP POST and integrate it with GraphQL Playground.

For this type of use cases I would recommend to use graphql-go/handler which handles both HTTP verbs: GET & POST.

Using graphql-go/handler and the examples/todo schema, both can be integrated to have GraphQL Playground working, Eg:

package main

import (
	"log"
	"net/http"

	"github.com/graphql-go/graphql/examples/todo/schema"
	"github.com/graphql-go/handler"
)

func main() {
	h := handler.New(&handler.Config{
		Schema:     &schema.TodoSchema,
		Pretty:     true,
		GraphiQL:   false,
		Playground: true,
	})

	http.Handle("/graphql", h)
	log.Println("server running on port :8080")
	http.ListenAndServe(":8080", nil)
}

[chris-ramon]

I went ahead and sent a PR#574 for exposing the TodoSchema so it can be use as shown above.

[chris-ramon]

Closing this one in favor of: #574