docs; add toObject to reserved list
benchmarks
docs; added examples of overriding `strict`

in doc.set and Model.update
docs; shardKey
fixed; empty object mixed defaults

Now interpreted as functions that return new empty objects.

To restore old behavior (a shared object between all documents)
set the "shared" option to true.

  new Schema({ data: { type: Mixed, default: {}, shared: true }})

fixes #1380
docs; document#populate()
docs; document#populated()