Builtin query method

[zbyte64]

Currently the user has to construct a Query object separately. The client should have a helper method to make this process more natural. Borrowing from typical ORM design it would be something like:

var query = client.query('widget').where({color: 'red'});
var widgets = query.fetch();

fetch would return an iterator from the blessed method created in #2

When es6 proxy objects happen, we might be able to do away with the need to explicitly call fetch.

[dmpayton]

I could see a client.query() method that returns a Query instance, but I'm not sure about query.fetch(). Query objects have no knowledge of the client instance.

Since we're already using the client to instantiate a query, is it that onerous to call client.execute(query=query)?