Mokkari

Changes since last release:
- Add support for upc field and variants.
- Moved build system to use poetry and other house-keeping changes.

Changes since last release:
- Update IssueSchema for new fields (price, sku)

Changes since last release:
- Handle series without a year_end date correctly.
- Add 'name' to the series schema.

Changes since last release:
- Use ' display_name' instead '__str__' for series list name results.

Changes since last release:
- Use correct version in user-agent string. Fixes 1
- Added connection error handling to api request.
- **API Change** changed IssueSchema 'name' field to 'story_titles'
- **API Change** added 'issue_name' field to IssueSchema
- **API Change** changed SeriesSchema 'publisher' field to 'publisher_id'
- Documentation improvements

Changes since last release:
- Add __getitem__ to list classes.
- Add some type hinting to code.