Document new date/time related functions.
Document new date/time related functions.

du2016/prometheus-docs,open-falcon/open-falcon.github.io,chosenken/docs,chosenken/docs,tcolgate/docs,du2016/prometheus-docs,prometheus/docs,ddfreyne/prometheus-docs,chosenken/docs,prometheus/docs,open-falcon/open-falcon.github.io,Cepave/openfalcon.io,tcolgate/docs,prometheus/docs,du2016/prometheus-docs,tcolgate/docs,ddfreyne/prometheus-docs,Cepave/openfalcon.io,Cepave/openfalcon.io,ddfreyne/prometheus-docs,open-falcon/open-falcon.github.io,ddfreyne/prometheus-docs,chosenken/docs