Order

- Add DotAccessProxy 'n' to UniqueObjectIndex. (4003698)
- Add object position lookup to unique object index. (5db770d)
- Add named ops to join_{root,numexpr}_selection util. (faca530)

- Make aux proxy object callable. (0e63628)
- Add custom x_labels to Variable. (cbbb8f5, 7de48e0)
- Parse hex strings in ColorMixin. (148c016)
- Add sorting operators to UniqueObject. (baf45ba)
- Let Dataset inherit from TagMixin. (43395ba)
- Allow initial objects to be passed in UniqueObjectIndex init. (ebea663)
- Fix indefinite recursion in DotAccessProxy. (7bb8955)

* Updated the `x` property of `AuxDataMixin`. Now, it returns a proxy object that provides simple attribute access to auxiliary data fields. See the [docs](https://python-order.readthedocs.io/en/latest/api/mixins.html#order.mixins.AuxDataMixin.x) for more info.

API changes

- `is_leaf_<name>`and `is_root_<name>` methods on UniqueObject's in trees are attributes now.

Features

- Added Python 3.8 support and test.

- Updated scinum dependency to >= 1.0.2

- Fixed pypi style.