Refdict

>Using a string as the keys of the partial result instead of storing the partial result in a variable. In this way the representation of refdict is correct.

Fixed

- Representation of partial refdict.

Fixed

Optimize documents.

Added

- Chain creation, just like creating new items in `dict`
- `rd = refdict({}); rd['a.b'] = 1` will cause `rd = refdict({'a': {'b': 1}})`

Added

- Method `refdict.get(keys, default = None)`, just like `dict.get` but can be used with chain keys.

Fixed

- The `str()` function.
- The `repr()` function.

Added

- Class method `findItem` to make non-refdict object has chain access and reference access effect.
- `refdict.findItem(data, 'key1.key2')`.
- Solution to use chain access and reference access many times with operator `()`.
- Operator `[]` will return a non-refdict object, so we can **NOT** use chain access or reference access after the first `[]`.
- But operator `()` will return a **sub-refdict**, which contains all data of the original refdict, but stand for a part of the original refdict.
- Finally, after querying sub-refdict using `()`, we need to use `[]` to get a non-refdict value.
- So we can use chain access and reference access many times like `rd('key1.key2')('key3.key4')['key5.key6']`.

Changed

- To realize sub-refdict, the member variable `refdict.data` become private. You have to use `refdict.load` to change the inner data of a refdict.

Added

- Support for chain containment check.
- `'key1.key2' in refdict({'key1':{'key2':123}}) => True`.