#### Is this adding or improving a _feature_ or fixing a _bug_?
Debt.
#### What's the new behavior?
This removes almost all existing deprecations from previous API changes, to save on filesize and reduce complexity in the codebase going forward.
It also changes from using the `slate-dev-logger` to using the Facebook-inspired `slate-dev-warning` which can be compiled out of production builds with [`babel-plugin-dev-expression`](https://github.com/4Catalyzer/babel-plugin-dev-expression) to save even further on file size.
The only deprecations it keeps are in the `fromJSON` methods for data model changes like `.kind` and `.leaves` which may still may not have been migrated in databases, since this is a bigger pain point.
#### Have you checked that...?
* [x] The new code matches the existing patterns and styles.
* [x] The tests pass with `yarn test`.
* [x] The linter passes with `yarn lint`. (Fix errors with `yarn prettier`.)
* [x] The relevant examples still work. (Run examples with `yarn watch`.)
#### Does this fix any issues or need any specific reviewers?
Fixes: #1922Fixes: #2105Fixes: #646Fixes: #2109Fixes: #2107Fixes: #2018
#### Is this adding or improving a _feature_ or fixing a _bug_?
Improvement.
#### What's the new behavior?
This introduces two new models: `Decoration` and `Selection`, which both implement the simpler `Range` interface. This way we can introduce properties to these concepts without having to have them live on all ranges, and we can start to introduce more helpful methods specific to each one's needs.
It also means we don't need to move `isFocused` to value, which saves some complexity on the operations side, retaining `set_selection` as the only way selections are modified.
In the process, it also cleans up a lot of the existing model logic for implementing the `Node` interface, and introduces another `Common` interface for shared properties of all Slate models.
#### How does this change work?
It introduces a new `interfaces/` directory where common sets of properties can be declared, and mixed in to the models with the new (simple) `mixin` utility.
#### Have you checked that...?
* [x] The new code matches the existing patterns and styles.
* [x] The tests pass with `yarn test`.
* [x] The linter passes with `yarn lint`. (Fix errors with `yarn prettier`.)
* [x] The relevant examples still work. (Run examples with `yarn watch`.)
#### Does this fix any issues or need any specific reviewers?
Fixes: #1952Fixes: #1807
Fixes: https://github.com/ianstormtaylor/slate/issues/2110
#### Is this adding or improving a _feature_ or fixing a _bug_?
Feature.
#### What's the new behavior?
This pull request adds paths to `Range` objects, including the selection. The paths and keys are kept in sync automatically, so that you can use whichever is ideal for your use case.
This should allow us to use paths for lots of the internal logic, which are much quicker to work with than keys since they avoid having to lookup the key in the document and can just traverse right to the node in question.
#### How does this change work?
`Range` objects have two new properties:
```js
range.anchorPath
range.focusPath
```
(Eventually these will be `range.anchor.path` and `range.focus.path` when points are introduced.)
When operations occur and whenever ranges are created/normalized, the paths are updated and kept in sync with the keys.
#### Have you checked that...?
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Please run through this checklist for your pull request:
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* [x] The new code matches the existing patterns and styles.
* [x] The tests pass with `yarn test`.
* [x] The linter passes with `yarn lint`. (Fix errors with `yarn prettier`.)
* [x] The relevant examples still work. (Run examples with `yarn watch`.)
#### Does this fix any issues or need any specific reviewers?
Fixes: https://github.com/ianstormtaylor/slate/issues/1408
Fixes: https://github.com/ianstormtaylor/slate/issues/1567
