Reflect to proxy object, to observe changes made by setters

[tomalec]

For example, to be able to observe the change made to obj.foo by setting obj.bar='new'

let obj = {
  'foo': 'old'
};
Object.defineProperty(obj, 'bar', {
  set: function (newValue) {
    this.foo = newValue;
  },
  get: function () {
    return this.foo
  },
  enumerable: true
});

Before this PR, this in setter was referring to original object not the proxy.

This change decreases performance significantly. According to npm run bench executed 3 times on my local it's:

jsonpatcherproxy generate operation -20,97%
jsonpatch generate operation -6,31%
jsonpatcherproxy mutation - huge object -5,12%
jsonpatch mutation - huge object -5,21%
jsonpatcherproxy generate operation - huge object -9,18%
jsonpatch generate operation - huge object -1,73%
PROXIFY big object -1,05%
DIRTY-OBSERVE big object -5,67%

[tomalec]

We can argue, that JS object with setter is not a JSON, therefore, we should not compromise performance for non-standard object.

[alshakero]

React Easy State does not make this sacrifice.

See "Avoid using the this keyword in the methods of your state stores."

https://github.com/solkimicreb/react-easy-state

[warpech]

It was discussed on a HO between me and @tomalec that we should introduce 2 modes of operation in JSONPatcherProxy:

• fast that does not reflect the proxy object to get and set operations. In fact, it does not need to use the Reflect API at all, it can use a quicker method: tree[key] = newValue.
• slow that reflects the proxy object to get and set operations. It must use the Reflect API

I can volunteer to do this change, but only if PR #42 is accepted first. Otherwise I would go nuts with the tests :)

[warpech]

This PR was rebased on current master and is now available as a new PR #44