LinkedList as parent of Option

The type Option is kind of weird:
```m2
i1 : new Option from {1,2,3}

o1 = 1 => 2

o1 : Option

i2 : peek oo

o2 = Option{1, 2, 3}

i3 : 1 => 2 => 3

o3 = 1 => 2 => 3

o3 : Option

i4 : peek oo

o4 = Option{1, 2 => 3}
```
I think something more useful would be a generalization like `LinkedList` that behaves like this:
```m2
i1 : new LinkedList from {1,2,3}

o1 = 1 => 2 => 3

o1 : LinkedList

i2 : 1 => 2 => 3

o2 = 1 => 2 => 3

o2 : LinkedList

i3 : peek oo

o3 = LinkedList{1 => 2}
2 => 3
```
This could be implemented internally simply as a hash table or even an actual linked list.

Start by locating the existing Option type and its peek behavior, then compare them with the proposed LinkedList examples. Define how construction from a sequence, chained arrows, and peek should behave, and consider whether the internal representation should be a hash table or linked list; the examples in the issue describe the expected result.

Written by the indexing model from the issue text.