Persist open file and location in file.

[Flyffies]

It would be a nice feature to reopen the file that was open when Docdown gets closed.

It would additionally be very helpfull to even scroll back to the last position.

If you really want to get fancy you could do the same for the PDF and even the file tree :)

[msujew]

Docdown now saves the current workspace state as of 531be6a. It reopens all files, scrolls back to the last position and also opens folders in the file tree. Sadly, because of an architectural limitation, this does not work for PDF files.

[msujew]

Apparently, it does not always scroll correctly, therefore I'll open up the issue again