Comicbox

- Fix parsing and writing genre, story_arc, series_groups tags

- Make metadata read more robust by catching individual tag exceptions and
printing them to stdout
- Protect against null people names for credits
- More robust xml volume parsing

- Fix cli crash with bad import

- Fix relative imports
- Fix credit parsing errors
- Improve 1/2 Issue number parsing

- Don't crash import on bad credits

- initial release