* Added mish layer doc opset
* Refactoring mish spec
* Update mish spec
* Change output description of Mish layer
* Fix Mish according to review
* Refactoring Mish and GELU spec according to code review
* Update formula for ops in spec
* Refactoring spec text
* Update Mish opset
* Change Mish version from 1 to 4
* Sort opset4
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