Feature request: possibility to use several document ids

[robertohuertasm]

We've been asked to support multiple document support.

This would basically imply that we can get files from more than one source.

The first implementation should deal with some cases:

• what happens if the image name is repeated in several documents?
  • For the moment we overwrite the image.
  • It would be nice to log this or warn the user about this.
  • We discarded having a nested directory structure like 1x > doc1, > doc2, >doc3