Multiple page PDF is taking too much resources

[garusis]

I try to convert a 42 pages pdf and It kill my laptop. I think that can be fix it if we add a property to limit the max quantity pages that can be process at time.

[marxys]

The issue come from var pageCount which have a wrong incredibly long value. I fix it on my pull request : #19

Your solution is useful to larger pdf, but can you add an offsetPage attribute to be able to continue treatment after first pass ?

[garusis]

Actually, the issue come from the pages' quantity that try to process at same time, but your fix is very useful and necessary. I'll try to integrate this with your PR when I have free time.