Add third party library to handle POST/GET request with batch and uploads feature

[jpascal]

Middleware and an Upload scalar to add support for GraphQL multipart requests (file uploads via queries and mutations) to various golang GraphQL servers.

Usage

server := &http.Server{
	Addr: "0.0.0.0:5000", 
	Handler: handler.New(func(request *handler.Request) interface{} {
		return graphql.Do(graphql.Params{
			RequestString:  request.Query,
			OperationName:  request.OperationName,
			VariableValues: request.Variables,
			Schema:         schema.New(),
			Context:        request.Context,
		})
	}, &handler.Config {MaxBodySize: 1024}),
}
    server.ListenAndServe()