Add Windows installation instructions for binary distrib.
Update config with version markers and users_db_public option.
Add auth API references for config. Small cleanup.
More inner references.
Split changelog.rst into group of per release branch articles.

Easy to track. Easy to support. Easy to autogenerate.
Changes are synced with 1.4.x branch.
Added 1.2.1 and 1.2.2 changes.
Sort changes by issue number in asc order.

Much more easy to navigate over them in this way.
Import breaking changes and upgrade notes from wiki.
Add MacOS installation guide.