Add outline entries for pages in existing PDF files

[edman193]

Hi, thanks for this great library. We used it to generate some great reports dynamically and it works very well.

I had the need to generate outline entries dynamically for the documents, and I want to share this functionality.

closes #134

Examples

To generate a single flat outline:

pdf = CombinePDF.new
i = 1
CombinePDF.load("file.pdf").pages.each do |page|
  pdf.add_outline_item(page, "Page #{i}")
  pdf << page
  i += 1
end
pdf.save "outlines.pdf"

Generating a tree hierarchy:

pdf = CombinePDF.new
i = 1
CombinePDF.load("file.pdf").pages.each do |page|
  if i.eql? 1
    pdf.add_outline_grouper(page, 'Section 1')
    pdf.add_outline_grouper(page, 'Subsection 1.1')
  elsif i.eql? 3
    pdf.go_out_outline_grouping_level
    pdf.add_outline_grouper(page, 'Subsection 1.2')
  elsif i.eql? 4
    pdf.go_outline_root
    pdf.add_outline_grouper(page, 'Section 2')
  elsif i.eql? 5
    pdf.go_out_outline_grouping_level
  end

  pdf.add_outline_item(page, "Page #{i}")

  pdf << page
  i += 1
end
pdf.save "outlines.pdf"

This will generate something like: