The Big List of Things to Scrape

As promised here's the big list of things to scrape AO3 for, as based on the python API, with some of my wishes as well. Feel free to rename things, or to add to this list as we go.

### Works
- [x] workid_from_url - grabs the workid from an AO3 URL
- [x] Work - sets the fic you're working with using the ID
- [x] work.title
- [x] work.url - if you have a workid, but not a URL, it will recompile the URL for you
- [x] work.series
- [x] work.series.id - gets the series ids associated with the fic
- [x] work.authors
- [x] work.authors.username
- [x] work.tags
- [x] work.nchapters - number of chapters posted
- [x] work.expected_chapters
- [x] work.fandoms
- [x] work.relationships
- [x] work.characters
- [x] work.language
- [x] work.categories
- [x] work.summary
- [x] work.rating
- [ ] work.get_images - gets the images posted in the fic
- [x] work.date_published
- [x] work.date_updated
- [x] work.status
- [x] work.warnings
- [x] work.words
- [x] work.hits
- [x] work.kudos
- [x] work.bookmarks
- [x] work.comments - number of comments only

### Chapters
- [x] chapter.id
- [x] chapter.url
- [x] chapter.title
- [x] chapter.summary
- [x] chapter.number
- [ ] chapter.words
- [x] chapter.number

### Series
- [x] series.id
- [x] series.url
- [x] series.name
- [x] series.words
- [x] series.creators
- [x] series.creators.username
- [x] series.description
- [x] series.notes
- [x] series.complete
- [x] series.series_begun
- [x] series.series_update
- [x] series.nworks - number of works in the series
- [x] series.work_list - a list of every work in the series
- [x] series.work_list.title - a list of only the titles in the series
- [x] series.work_list.url - a list of the URLs of the fics in the series

### User
- [x] user.bio
- [x] user.works
- [x] user.bookmarks
- [x] user.url
- [x] user.get_avatar

### Errors
- [x] #138
- [x] AuthError - must be registered user to see work