Add: Finalise and complete the modify methods

[dxinteractive]

Kinda sorta proposed API

modifyDown() and modifyUp()

simple value-in value-out like ii => ii * 2

parcel
    .modifyDown(num => `${num}`)
    .modifyUp(str => Number(num))

modifyShapeDown() and modifyShapeUp()

Gives you a StaticParcel (immutable.js-like parcel that doesnt have the two way binding), expects a StaticParcel to be returned.

parcel.modifyShapeDown(staticParcel => staticParcel
    .push(123)
    .push(456)
    .setMeta({abc: 789})
);

modifyChange()

Gives you a parcel and a change request, diy action editing and dispatching madness if you really need control of action order and stuff.

Modify methods

The modify methods allow you to modify the data in a parcel in the middle of a chain of parcel function calls, without affecting the parcels real value. The data can be edited on the way down, when the parcel component is rendered; or on the way up, once a change takes place and a new value is being sent back up.

Their primary usage is if you need to store one kind of value in the parcel itself, but edit

[dxinteractive]

The above proposed API was changed heavily before release, please read the docs for the end result. Released in https://github.com/blueflag/dataparcels/releases/tag/v0.18.0