[Scilab-Dev] Switch to use Markdown for CHANGES

[Clément David]

Dear Scilab contributors,

For the (near to be released) beta-2, I updated the CHANGES files to use the Markdown format [1].
The idea is to be able to generate some document (html and pdf) from it in a semi-automatic way.
Another point would be to have it nicely formatted on hosting platforms (github/gitlab) that render
markdown on the fly.

What do you think about that ? It is currently not clear to me if we should add an empty line
between each `*` and if we should use set bugzilla URLs.

[1]: https://codereview.scilab.org/#/c/18222

Thanks for your remark,

PS: for the beta-2, we will probably push it but any modification is possible for the stable
release.

--
Clément