Start using Changelog in Github projects

[Marko Sagadin]

Context

A changelog is a file which contains a curated, chronologically ordered list of notable changes for each version of a project.
Changelog makes it easier for users and contributors to see precisely what notable changes have been made between each release (or version) of the project.

Goal

Start using [KeepAChangelog}(https://keepachangelog.com/en/1.0.0/) format for changelog document.
Define few guidelines that say what should be written in the changelog document.
Create a document, and keep it in a irnas-core.
This document should be referenced by the each changelog file, each project's README should mention that changes are kept in a changelog file.

[Marko Sagadin]

This was done.