Updating news, readme files and bumping master version to 1.3.1

[Roshrini]

Description

As title
Please do not merge until after the release.
@szha

@gigasquid I did not include clojure files here as I was not sure about them. Can you please point those out?

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

[gigasquid]

Thanks for putting this together @Roshrini.
The version number is located in the project.clj files in the Clojure package.

• https://github.com/apache/incubator-mxnet/blob/master/contrib/clojure-package/project.clj#L18 - The main one
• And one for each of the examples directory project.clj dependencies. For example here
  https://github.com/apache/incubator-mxnet/blob/master/contrib/clojure-package/examples/cnn-text-classification/project.clj#L22
• and finally the README should be updated to point to the right 1.3.0 instead of 1.2.1 maven jars

I'd be happy to put a separate PR together for it if you prefer.

[Roshrini]

@gigasquid Updated clojure files.

[gigasquid]

I tested the clojure package and it looks great 💯

[kalyc]

Thanks for your contribution @Roshrini
@mxnet-label-bot[pr-awaiting-review]