Factorize configuration files across projects

[AntoineRondelet]

This issue is not directly related to Zeth, but rather concerns:

• Zecale
• Libsnark/ff
• Zeth

These projects use cmake and hold rather similar versions of files in the cmake directory. While there is value to have these files replicated in each projects (each project has its own configuration), in many cases the files in cmake/ remain untouched and are project independent. Duplicating these files is increasing the chances of inconsistencies across projects (e.g. a make target is renamed on zeth but the content of cmake/ isn't updated on the other repos). There may be value to try to factorize these config files in one location that is shared across all repos. Let's think about that.

[AntoineRondelet]

Similar thing for files like CODING_STANDARDS.md, CODE_OF_CONDUCT.md, and CONTRIBUTING.md. These could be hosted on a Github repo to which we link in the individual's README's to avoid duplication of these files and keep them consistent. These files can act as "parent/default" files and can be overwritten on a case by case basis in the specific repos, as needed, as we do in Zecale for instance: https://github.com/clearmatics/zecale/blob/master/CODING_STANDARDS.md#coding-standards