Tests to prove specification is respected

This is a list of things we need to test to make sure the adapter abides to JSONAPI.org.

- [x] Individual Resource Representations
- [x] Resource Collection Representations
- [ ] Resource Types
- [ ] ~~Resource URLs~~
- [x] To-One Relationships
- [x] To-Many Relationships
- [ ] ~~URL Templates~~
- [x] Compound Documents
- [x] URLs for Resource Collections
- [x] URLs for Individual Resources
- [ ] ~~Relationship URLs~~
- [x] Creating an Individual Resource
- [ ] Creating Multiple Resources
- [x] Updating an Individual Resource
- [ ] Updating Multiple Resources
- [ ] Updating Attributes
- [ ] Updating To-One Relationships
- [ ] Updating To-Many Relationships
- [ ] Deleting To-One Relationships
- [ ] Deleting To-Many Relationships
- [ ] Deleting Resources
- [ ] Errors

~~Strikethrough~~ text is not planned for this PR.