PaginatedList redux

[jessemcbride]

Modify PaginatedList to provide support for special methods on some CanvasObject types:

• len
• negative indexing

[Thetwam]

See discussion on #237 (review) for limitations on implementation

[jessemcbride]

See https://gist.github.com/jessemcbride/133312e5af9e6eb1de7d5b77dc9b7ba9 for implementation scaffolding.

[jonespm]

Was this still being worked on? I think just knowing the number of pages and items in a list, which is often available from the last link and available via a calculation of per_page would be really useful for api calls that have tons of pages. The scaffolding example is kind of how I was thinking this would go. I'm less concerned about the negative index than just being able to estimate how long processing will take. Thanks for adding this!