* sketching out changes needed to integrate variables into DataTree

* fixed some other basic conflicts

* fix mypy errors

* can create basic datatree node objects again

* child-variable name collisions dectected correctly

* in-progres

* add _replace method

* updated tests to assert identical instead of check .ds is expected_ds

* refactor .ds setter to use _replace

* refactor init to use _replace

* refactor test tree to avoid init

* attempt at copy methods

* rewrote implementation of .copy method

* xfailing test for deepcopying

* pseudocode implementation of DatasetView

* Revert "pseudocode implementation of DatasetView"

This reverts commit 52ef23b.

* removed duplicated implementation of copy

* reorganise API docs

* expose data_vars, coords etc. properties

* try except with calculate_dimensions private import

* add keys/values/items methods

* don't use has_data when .variables would do

* explanation of basic properties

* add data structures page to index

* revert adding documentation in favour of that going in a different PR

* explanation of basic properties

* add data structures page to index

* create tree node-by-node

* create tree from dict

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* dict-like interface

* correct deepcopy tests

* use .data_vars in copy tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* black

* whatsnew

* data contents

* dictionary-like access

* TODOs

* test assigning int

* allow assigning coercible values

* simplify example using #115

* add note about fully qualified names

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

…ntrib/datatree#115

* test assigning int

* allow assigning coercible values

* refactor name-related methods to intermediate class

* refactor tests to match

* fix now-exposed bug with naming

* moved test showing lack of name permanence

* whatsnew