#### FEATURES
* use `ContentState` instead of `EditorState`, selection events won't trigger
onChange anymore.
* deprecated `Mention.toEditorState`, instead of `Mention.toContentState`,
* `Mention.toEditorState` are compatibled, but have a warnning in console.
#### ISSUES
* `disabled` and `readOnly` props supported.
* fixed controlled mode bug.
* close#5788
* close#5175
* close #https://github.com/react-component/editor-mention/issues/7
+ add `getSuggestionContainer` callback function, which allow users modify the
container element of suggestions dropdown.
+ the suggestions dropdown will mount on `document.body` defaultly, instead of
on editor.
+ close#3588
