Create DocHandle with an initial document

[acurrieclark]

Either

• pass an initial value and do something like this to ensure that you get a valid initial value

const myInitialValue = {
  tasks: [],
  filter: "all",

const guaranteeInitialValue = (doc: any) => {
if (!doc.tasks) doc.tasks = []
if (!doc.filter) doc.filter = "all"

  return { ...myInitialValue, ...doc }
}

or

• pass a "reify" function that takes a <any> and returns <T>

[acurrieclark]

Closed by #274