Added unique set

ethutil/set.go

+package ethutil
+
+type Settable interface {
+	AsSet() UniqueSet
+}
+
+type UniqueSet map[interface{}]struct{}
+
+func NewSet(v ...interface{}) UniqueSet {
+	set := make(UniqueSet)
+	for _, val := range v {
+		set.Insert(val)
+	}
+
+	return set
+}
+
+func (self UniqueSet) Insert(k interface{}) UniqueSet {
+	self[k] = struct{}{}
+
+	return self
+}
+
+func (self UniqueSet) Include(k interface{}) bool {
+	_, ok := self[k]
+
+	return ok
+}
+
+func Set(s Settable) UniqueSet {
+	return s.AsSet()
+}