v2.6.3

Changed:

• OCRD-ZIP: Ocrd-Mets and mets:FLocat URI/paths must be relative to /data, #99
• OCRD-ZIP: Ocrd-Mets only relevant for extraction
• OCRD-ZIP: Filenames MUST be relative to mets.xml
• METS: Filenames MAY/SHOULD be relative to mets.xml
• OCRD-ZIP: Allow a limited set of files in the bag basedir (readme, build files), #97