Support YAML/JSON configuration file

[zhenghaoz]

Gorse uses https://github.com/spf13/viper to load the configuration file, which supports YAML and JSON format as well:

gorse/config/config.go

Lines 550 to 555 in 492ffbb

	// load config file
	viper.SetConfigType("toml")
	viper.SetConfigFile(path)
	if err := viper.ReadInConfig(); err != nil {
	return nil, errors.Trace(err)
	}