Add ImmutableLinkedList#isEmpty
Add ImmutableLinkedList#head
Add ImmutableLinkedList#tail
Add ImmutableLinkedList#subList
Refactor ImmutableLinkedList#tail using ImmutableLinkedList#subList
Add ImmutableLinkedList#iterator
Refactoring using iterators
Add ImmutableLinkedList#map
Add ImmutableLinkedList#any and ImmutableLinkedList#all
Merge branch 'linkedlist'