move "HTTP PATCH" paragraph into "Upgrading 3.2 -> 4.0". [ci skip]
3.2 to 4.0 section in upgrading guide is no longer wip. [ci skip]
create 4.1 release notes guide scaffold. [ci skip]
first pass through CHANGELOGS to extract 4_1_release_notes. [ci skip]

Extract **notable changes**, **deprecations** and **removals** from
each CHANGELOG.

I tried to reference the commits and pull requests for new features
and deprecations.

In the process I also made some minor changes to the CHANGELOGS.

The 4_1_release_notes guide is declared WIP.