Feature request: support saving chart as PDF

[surban]

Currently it seems impossible to save a chart as a PDF or EPS file. Changing the extension in the Chart.Save command from .png to .pdf still results in a PNG file. PDF should be supported as the format is a much better fit for vector data than PNG and widely used in (scientific) publishing.

[simra]

Since there is no native support for saving a bitmap as PDF, I think the solution here is to provide a print facility and allow the user to print-to-pdf. I had a quick look at feasibility and it's more than just a few lines of code, but it seems doable.