ObserverList class

1. Constructors
2. ObserverList
3. Properties
4. isEmpty
5. isNotEmpty
6. iterator
7. first
8. hashCode
9. last
10. length
11. runtimeType
12. single
13. Methods
14. add
15. contains
16. remove
17. any
18. cast
19. elementAt
20. every
21. expand
22. firstWhere
23. fold
24. followedBy
25. forEach
26. join
27. lastWhere
28. map
29. noSuchMethod
30. reduce
31. singleWhere
32. skip
33. skipWhile
34. take
35. takeWhile
36. toList
37. toSet
38. toString
39. where
40. whereType
41. Operators
42. operator ==