v2.27.0

Fixed:

• remove dependency on six, #732
• ocrd workspace remove-group: handle files not in subdir gracefully, #734
• ocrd resmgr: fix "reference before assignment" issue #689, #733
• OcrdWorkspace.remove_file: handle empty regexes, #725

Changed:

• ocrd workspace rename-group will now also rename filenames and mets:file/@ID, #736