Added Immutable userlist

list/immutable.go

@@ -0,0 +1,17 @@
+package list
+
+// An Immutable is a wrapper around a userlist reference that provides a limited
+// set of methods for reading a userlist's content
+type Immutable struct {
+	list *List
+}
+
+// User gets a user by nick
+func (il Immutable) User(nick string) (u User, ok bool) {
+	return il.list.User(nick)
+}
+
+// Users gets all the users in the list, in order
+func (il Immutable) Users() []User {
+	return il.list.Users()
+}