func (s StringSet) Includes(value string) bool {
	_, ok := s[value]
	return ok
}
Includes returns true if the receiver contains value
package set
type StringSet map[string]struct{}
func Strings(values []string) StringSet {
	s := make(StringSet)
	for _, str := range values {
		s[str] = struct{}{}
	}
	return s
}
func OfStrings(strings ...string) (s StringSet) {
	return Strings(strings)
}
func (s StringSet) Len() int {
	return len(s)
}
func (s StringSet) AsSlice() []string {
	result := make([]string, len(s), len(s))
	i := 0
	for v := range s {
		result[i] = v
		i++
	}
	return result
}