func ParseConfigFromGr(filename string) (internal.Config, error) {
	f, err := os.Open(filename)
	if err != nil {
		return internal.Config{}, err
	}
	defer f.Close()
	decoder := json.NewDecoder(f)
	var config config
	if err := decoder.Decode(&config); err != nil {
		return internal.Config{}, err
	}
	return internal.Config{
		Source:     internal.JsonSrc,
		LoadedFrom: filepath.Dir(filename),
		Tags:       map[string][]string(config.Tags),
	}, nil
}
ParseConfigFromGr tries to parse an config file from the
original mixu/gr json config.
package gr
import (
	"github.com/kernle32dll/ew/internal"
	"encoding/json"
	"os"
	"path/filepath"
)
type config struct {
	Tags tags `json:"tags"`
}
type tags map[string][]string