Fetch the model using an array. Also laid the groundwork for the ability to specify three different types of where-clauses... in addition to searching by an array, we'll have the ability to search using the primary key and a custom WC.

search by array example:
new Person(array("person_id"=>1,"firstname"=>"andrew"));

search by primary key example:
new Person(1);

search by custom example:
new Person("person_id=1 AND firstname=andrew");