Adding unstable and fixing #250, #249 and #248

[PonteIneptique]

• Removed totalItems from the Collection Endpoints (See https://github.com/distributed-text-services/specifications/issues/248, problem pointed out by @kbrueckmann)
• passage property (URI template) moved to document for consistency between Collection and Navigation endpoint (See https://github.com/distributed-text-services/specifications/issues/249, problem pointed out by @philippepons)
  • Harmonized the examples to have the resource already populated, as per Collection URI Templates
• collection property (URI template) added to Collection and Resource object (See https://github.com/distributed-text-services/specifications/issues/250, problem pointed out by @philippepons)
• Fixed a typo in the Entry endpoint table, where it referenced Resources.

@hcayless There is some form of discrepancy in URI template uses in example. Sometime there are IDs filled, sometimes not. I think I tried to make the most sense out of it but... :)