New support for including the document in each view row

[cmbrandenburg]

Add support for the include_docs query parameter when executing a view. Doing so will require changing the ViewRow type to optionally contain a Document.

It might be a good idea—either now or later—to make a new reference-counted document path type, similar to DocumentPath, whereby the database name component is stored as a std::rc::Rc<DatabaseName>. Otherwise, each view row containing a document will have a copy of the same database name, which could lead to a lot of allocations. I envision the reference-counted document path type to be an private type inside Chill.

The reference-counting idea is probably a bad idea. The std::rc::Rc type implements !Send, meaning Rc prevents anything containing it from moving to another thread. Having a Document (or ViewRow) contain an Rc would be prioritizing for efficiency over convenience—contrary to the central aim for Chill. For this specific case, it would be better merely to incur the cost of one extra allocation per document for the database name, as that cost will be lost in the noise of doing an HTTP round-trip with the CouchDB server.

[cmbrandenburg]

ViewResponseBuilder should be updated to support document inclusion for each row being constructed.