Cobalt

- Parser now accepts both strings and bytes, and will encode strings to bytes using UTF-8

- Rename `DebateReport` to `Debate`

- Add new schemas.AkomaNtoso30 class with basic schema information

- Add support for portions, such as `~chp_2`
- Remove non-standard support for expression component and
subcomponent
- Remove non-standard legacy support for work components without `!`

- Allow slashes in FRBR URI work component names
- Setting expression and manifestation dates updates attachments and
other components
- Don\'t include Cobalt-specific `<references>` element in attachments
- Cascade changes to FRBRlanguage into attachments
- Don\'t hardcode source
- Don\'t set `contains="originalVersion"` since it is the default
value for that attribute.
- Use `0001-01-01` as a placeholder date for publication, amendment
and repeal events with null dates

- Change eIds of content produced by empty_document_content()