Fixes issue with confusion about features that has not been
released yet.
Move deveopment manual.yml to dev/manual.yml
Symlink manual.yml to v1.7/manual.yml
Refactor to share history header with links to other manual versions.
Change man.test and man page generation to use dev/manual.yml
Related to #3078#3127
The markdown python changed its API for markdown extensions.
Bumping the markdown package version in previous commits broke
docs/build_manpage.py since it was using registering an extension with
the old API.