v3.3.0

Added:

• Draft spec for logging
• Draft spec for provenance

Changed:

• ocrd-tool: Additional additional category layout/segmentation/text-image
• ocrd-tool: Remove syntactical restriction for content-type
• ocrd-tool: output_file_grp no longer required
• CLI: --mets and --working-dir are optional not required
• CLI: --output-file-grp is optional, OCR-D/core#296