Add skip options to find.
Limit batch size on find when the limit option is set.

This is to optimize query.
Add 'nin' and 'in' to query.

This methods are used with field name and array.

db.query().nin('fieldname',['a', 'b']);
db.query().in('fieldname',['a', 'b']);

Read below for more information.
http://docs.mongodb.org/manual/reference/operator/query/in/
http://docs.mongodb.org/manual/reference/operator/query/nin/
Fix bugs in collection.find().

QueryOpts is immutable, skip() and batchSize() doesn't change itself, it
creates new one.

Both skipN and batchSieN has default value 0.