Add method to query by Ids only

[sjurgis]

It would be rather useful to re-query db by a set of Ids without explicitly declaring type required - library should infer the types of record itself and also handle cases where set has mixed types.

Also might be useful to have a method to pass a collection of SObjects and it re-queries with same fields that have been passed in.

Very useful when doing async and you wanna check if database still has same records!