The log of significant changes prior the first release of GIL as part
of Boost was collected from https://stlab.adobe.com/gil/news.html site
and from the linked PDF documents with detailed descriptions.
The old history is very detailed (after the PDFs) but it is intersting.
It illustrates evolution of the library design and API, for example,
renaming of types or functions were renamed indicates evolution of
semantics and inter-relations of the library elements.
This is especially interseting in case of the complex types like
bit-aligned pixels and images, where does the concept of memunit
come from, etc.
This proposes to use Git to maintain notes about all notable changes to
GIL in `RELEASES.md` file based on https://keepachangelog.com format.
This implements proposal discussed and agreed in the thread
https://lists.boost.org/boost-gil/2019/11/0336.php
Collect all past release notes.
Collect release notes for the pending Boost 1.72.0, to be released
in December according to Boost release schedule.
