func Keys(m map[string]string) []string {
	return Contract(m, func(k string, v string) string {
		return k
	})
}
Keys extracts the key of a map[string]string and returns them
as a slice of strings.
package stringutils
func Transform(s []string, f func(string) string) []string {
	var transformed []string
	for _, e := range s {
		transformed = append(transformed, f(e))
	}
	return transformed
}
func Quote(s []string) []string {
	return Transform(s, func(str string) string {
		return `"` + str + `"`
	})
}
func DefaultIfEmpty(value, defaultValue string) string {
	return DefaultIf(value, defaultValue, "")
}
func DefaultIf(value, defaultValue, condition string) string {
	if value == condition {
		return defaultValue
	}
	return value
}