Add a function to find the last actual observation time, and use this to set the plot range in the example.
Add a function to find the last actual observation time, and use this to set the plot range in the example.

git-svn-id: acf0ef94bfce630b1a882387fc03ab8593ec6522@117 150532fb-1d5b-0410-a8ab-efec50f980d4

dopplershift/MetPy,Unidata/MetPy,jrleeman/MetPy,ahaberlie/MetPy,deeplycloudy/MetPy,Unidata/MetPy,jrleeman/MetPy,dopplershift/MetPy,ShawnMurd/MetPy,ahill818/MetPy,ahaberlie/MetPy