SAMZA-46
Improve the state management documentation.
Misc. tweaks to the state management docs at Tejas' suggestion.
Misc. improvements to the state management docs.
Merge branch 'SAMZA-25' of github.com:criccomini/incubator-samza into SAMZA-25
make counter and gauges injectable so we don't have to constantly set gauge values. set offset gauges in task instance using new method.