Cosmetic fixes to DFPackage.c comments
Word_to/fromPlain: Add rawPackage parameter

When converting from a plain text package to a WordPackage, also pass
back the raw DFPackage object, so that the caller can later use it to
get at the resulting package contents after modification.

When converting from a WordPackage to a plain text package, do so using
the DFPackage object.
WordPackage: Don't explicitly zip/unzip file

In WordPackage and OPCPackage, assume that the contents of the DFPackage
object can be loaded and save directly, without the need to first unzip
or zip the data from a file. This allows us to work with packages
resresented solely in memory, e.g. in the test cases. If the data is to
actually be stored in a physical .docx file (which is just a zip file),
then the code that uses WordPackage must manage this.

This is a temporary measure until we have a DFPackage implementation
that can work directly with zip files.