write (v3) tests that do (a lot) more for osullivan

[ndushay]

• tests that use the fixture objects?
• tests that ensure that given classes actually produce the desired json
  • abstract_resource (#19)
  • service (#20)
  • manifest (#22- WIP)
  • sequence (#24 - WIP)
  • canvas (#25)
  • annotation_page (#30)
  • annotation (#30)
  • resource (#29)
  • image_resource (#29)
  • range
  • choice (#30)
  • collection
  • annotation_collection

Chris's suggestion: borrow some code from purl to create a iiif presentation bits, and compare the created bits to expected bits.

Okay to add such tests only to v3 at this point, I would say.