Make a number of properties nullable. Replace CPTLayer HostedLayer property with CPTGraph HostedGraph property in class CPTGraphHostingView to reflect the same change that has been done in the underlying CorePlot framework.
Merge pull request #88 from ash23/master

Make a number of properties nullable. Replace CPTLayer HostedLayer property with CPTGraph HostedGraph property in class CPTGraphHostingView to reflect the same change that has been done in the underlying CorePlot framework.