API change proposal

Hi,
Thanks for maintaining the module! It's really important for our current project!

I'm proposing a small change to the Balance Tracker API, as currently the exposed hooks are not versatile enough to extend the module behavior with custom modules.

What I propose is, that the main debit and credit -functions and the two hooks use the $message -variable inside a $data -array. This data-array could then also be used for other modules to incorporate data important to them.

The way it works with other modules is, that the hook_balance_write would send the bid of the last written record. This way, if other modules want, they can call for example the balance_tracker_debit_account -function, add its own data into the data-array, and then act upon the hook_balance_write.

Example from my module:
Node Reference passed (notice the nid):

// Debit account
balance_tracker_debit_account($user->uid, $amount, array('message'=> "Message: ".$node->field_message[0]['value'], 'nid'=>$nid));

...

/**
 * Implementation of hook_balance_write()
 */

function bt_node_reference_balance_write ($bid, $uid, $type, $amount, $data) {
  // make sure we have the needed id's
  if($type != 'debit' && (!isset($bid) || empty($data['nid'])))
    return;
    
  // update  
  $success = db_query("UPDATE {balance_items} SET nid = %d WHERE bid = %d", array($data['nid'], $bid));

}

I'm releasing soon an add-on module for Balance Tracker called Balance Tracker Node Reference which would use this solution. I'm releasing the code once there's a decision for this change (and after I learn some git... :) )

I've added two patches that are built to the latest dev-release. It updates the current code for balance_tracker and bt_invite_commission to this proposed logic. Tested working on my site.