made it possible to post-process the generated pdf

[schmitch]

currently we add various xmp metadata / color profile
to the document. so it's really useful to get the pddocument.

[rototor]

This looks fine to me

[danfickle]

Thanks @schmitch

I have implemented an explicit createPDFWithoutClosing method while refactoring PdfBoxRenderer. Usage is something like below:

	public static void main(String... args) throws Exception {
		OutputStream os = new FileOutputStream("/Users/you/Documents/pdftests/mytest-159.pdf");
		PdfRendererBuilder builder = new PdfRendererBuilder();
		builder.withUri("file:///Users/you/Documents/pdftests/issue-159.htm");
		PDDocument doc = null;
		try (PdfBoxRenderer renderer = builder.buildPdfRenderer()) {
			renderer.createPDFWithoutClosing();
			
			doc = renderer.getPdfDocument();
			
			// ... post process doc.
			

		} finally {
			doc.save(os);
			doc.close();
			os.close();
		}
	}