hasMany setter uses bulk create and destroy to create and remove associations

[janmeier]

In response to #104

Since we now have bulk create and updates available, there is no reason to do individual queries for each object. Instead of

Executing: INSERT INTO `x` (`a_id`,`b_id`) VALUES (1,1);
Executing: INSERT INTO `x` (`a_id`,`b_id`) VALUES (2,1);

We will now do

Executing: INSERT INTO `x` (`a_id`,`b_id`) VALUES (1,1), (2,1);

And similarly for deletions:

Executing: DELETE FROM `x` WHERE `a_id`=1 AND `b_id`=1 LIMIT 1;
Executing: DELETE FROM `x` WHERE `a_id`=1 AND `b_id`=2 LIMIT 1;

Becomes

Executing: DELETE FROM `x` WHERE `a_id`=1 AND `b_id` IN (1,2);

[durango]

Can you do me a favor and add some simple tests to this such as checking for the "IN" part on the deletion as well as multiple values for inserts? This is not because of your code, but just in case someone makes a change down the road that breaks this.

[durango]

Can you fix this typo? :P