Add parent path to changes map

[derrell]

With an arbitrary set of object changes, including keys that contain dots or
slashes, it can be difficult to retrieve, via dot notation, an object whose
property is changing. Consider this set of operations:

let             test;
let             p;
const           ObservableSlim = require("./observable-slim.js");

test = {};
p = ObservableSlim.create(
  test,
  false,
  (changes) =>
    {
      console.log(JSON.stringify(changes, null, "  "));
    });

p.hello = "world";
p["a.b"] = { c : {} };
p["a.b"].c["e.f"] = 42;

The output of the final change is:

[
  {
    "type": "add",
    "target": {
      "e.f": 42
    },
    "property": "e.f",
    "newValue": 42,
    "currentPath": "a.b.c.e.f",
    "jsonPointer": "/a/b/c/e/f",
    "proxy": {
      "e.f": 42
    }
  }
]

Note that it is not exactly trivial to figure out how to update a remote
object based on this information. There is nothing here that would tell you
that of currentPath "a.b.c.e.f", the "a.b" part is a single key.

To help resolve this problem, I have added the parent path to the change
map. With the parent path, an array, it is easy to iterate through the array
beginning at the top-level object, to then add/update/whatever the given
property. With the change, the above test yields, as the final change, the
following, which includes the parent array member:

[
  {
    "type": "add",
    "target": {
      "e.f": 42
    },
    "parent": [
      "a.b",
      "c"
    ],
    "property": "e.f",
    "newValue": 42,
    "currentPath": "a.b.c.e.f",
    "jsonPointer": "/a/b/c/e/f",
    "proxy": {
      "e.f": 42
    }
  }
]

[coveralls]

Pull Request Test Coverage Report for Build 101

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 95.262%

---

Totals
Change from base Build 89:	0.02%
Covered Lines:	237
Relevant Lines:	237

---

💛 - Coveralls

[ElliotNB]

@derrell My sincere apologies for not seeing this until now! I'll take a look at this contribution this week or by early next week. One thing that I noticed right off the bat is the use of spaces instead of tabs for indentation. Would you be able to switch it to tabs on your fork?

[derrell]

@ElliotNB Sorry about the formatting issue. I try to be careful to match the format of code I'm changing, but obviously missed it here. Fixed now.

[BackdoorTech]

Looking cool!