Replace Document-based methods on Database class

[commana]

As part of our effort to introduce Jackson, the following methods on the Database class need to be deprecated:

• saveDocument
• bulkSaveDocument
• deleteDocument
• getDocument

Ideally, the Database should work with POJOs that are converted to JSON. For example, to save an object of type Entity, the following should transparently create a JSON representation that is written to the database:

Entity entity = ...
database.save(entity);
// entity now contains the updated _rev attribute