* Update HPA docs with more algorithm details
The HPA docs pointed to an out-of-date document for information on the
algorithm details, which users were finding confusing. This sticks a
section on the algorithm in the HPA docs instead, documenting both
general behavior and corner cases.
* Add glossary info, HPA docs on quantities
People often ask about the quantity notation when working with the
metrics APIs, so this adds a glossary entry on quantities (since they're
used elsewhere in the system), and a short explantation in the HPA walkthough.
* Information about HPA readiness and stabilization
This adds information about the new changes to HPA readiness and
stabilization from kubernetes/features#591, and other minor changes that
landed in Kubernetes 1.12.
* Update horizontal-pod-autoscale.md
Solly Ross
93c0bb9347