Convert files to papis documents

[alejandrogallo]

This pull request handles 3 cases

1. A single file gets moved into its own directory
   with an info.yaml file for it, together with
   the original file. The title of the papis document
   is original title of the file (without extension)
   and the names of the folders and files associated
   with the papis document is the title without whitespaces.

2. If a file comes in different formats (e.g. some pdf
   files have also a version in doc or ppt format),
   then both copies get moved into their own papis directory
   as explained in point 1.

3. Some html files have a directory related to them,
   this directory is moved as is to the papis folder.
   The rest is as in point 1.

The script used for this is also attached to the
pull request, file-to-papis.sh.

In the pdfs directory, you can try

papis -l . -s use-cache False -s opentool xdg-open open

and play around.

I'd gladly answer questions.
file-to-papis.sh.zip