* first stab at removing leaves with tests passing
* fixes
* add iterables to the element interface
* use iterables in more places
* update examples to use iterables
* update naming
* fix tests
* convert more key-based logic to paths
* add range support to iterables
* refactor many methods to use iterables, deprecate cruft
* clean up existing iterables
* more cleanup
* more cleaning
* fix word count example
* work
* split decoration and annotations
* update examples for `renderNode` useage
* deprecate old DOM-based helpers, update examples
* make formats first class, refactor leaf rendering
* fix examples, fix isAtomic checking
* deprecate leaf model
* convert Text and Leaf to functional components
* fix lint and tests
#### 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...?
<!--
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
* initial simple decorations (mark-like), many tests added
* allow decorators to be set by focus, anchor tags - add tests
* handle one more edge case with decorations in hyperscript
* apply prettier cleanup
* apply linting rules
* update changelog
* ensure always normalize decoration ranges
* reapply prettier after latest adjustments
* update in response to review
* drop unnecessarily committed add'l file
* remove the need for explicit anchor, focus prop on decoration tags
* Add failing test
* Don't push extra text node at the end of children
* Fix keys in tests
* Add option `normalize` to <value>
* Write Changelog
* Changelog on correct package
* Fix preserve keys test
* Fix tests (which make more sense now)
* Mark failing test as skipped
* Account for skip option
* Lint and fix changelog version
* Use Unreleased instead of version
* Lint markdown
