Smooth KullbackLeibler

[epapoutsellis]

Describe your changes

Implementation of Smooth version of KL:

• [ ] At this stage there is no numba implementation as we did in KL
• [ ] Missing unittests.
• [ ] Proximal method is not implemented yet.

Describe any testing you have performed

Please add any demo scripts to CIL-Demos/misc/ :

Link relevant issues

Checklist when you are ready to request a review

• [ ] I have performed a self-review of my code
• [ ] I have added docstrings in line with the guidance in the developer guide
• [ ] I have implemented unit tests that cover any new or modified functionality
• [ ] CHANGELOG.md has been updated with any functionality change
• [ ] Request review from all relevant developers
• [ ] Change pull request label to 'Waiting for review'

Contribution Notes

Please read and adhere to the developer guide and local patterns and conventions.

• [ ] The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in CIL (the Work) under the terms and conditions of the Apache-2.0 License.

[paskino]

It is clear we cannot accept a PR without unittests

[paskino]

closes #740