DO NOT MERGE YET (PDB-784) Final release changes for PDB 2.2.0

(awaiting release, don't merge it yet)

This pushes PuppetDB 2.2.0 to be the primary documentation, and fixes the index
so it references 2.2 instead of master (my mistake from last commit).

Signed-off-by: Ken Barber <ken@bob.sh>