Added "encode-as-base64" option to px:unzip-fileset

Useful if you want to read the file contents byte-for-byte.
For instance, you can use it to validate the XML declarations of zipped XML files.
Update zip-utils POM version

The API has changed, hence the MINOR version is increased.
Merge pull request #53 from daisy-consortium/bytewise-unzip

Also update the POM version. Close #53.