Release of OxyPlot.Core v2.0.0

We have released v2.0.0 of the oxyplot core repository. See the change log for details. The following NuGet packages have been updated:

• OxyPlot.Core
• OxyPlot.WPF
• OxyPlot.WindowsForms
• OxyPlot.Core.Drawing (new)
• OxyPlot.OpenXml
• OxyPlot.Pdf

Thanks to everybody who have contributed!