* ScatterElementsUpdate-12 init
* Update doc structure with ScatterElementsUpdate-12
* Update Operations_specifications.md
* Typos
* Update descriptions
* Add info about indices normalization
* Add info about negative axis normalization
* Add info about boolean type
* Missing coma and typo
* More examples and reduction descriptions
* Rename reduction "copy" to "none"
* Add more examples with values
* Mean mode and types clarification