Fixed issue where passing an object with multiple keys did not work correctly

Previously, passing an object with multiple keys did not work, this was due to the fact that the `finishedCallback` argument to the function was being overwritten (unintentionally) inside the check if `argument[0]` was an object.

By removing the explicit argument list in the function, and instead inferring the arguments directly from the arguments array, this now supports both passing explicity and as an object:

```
var finished = function() {...};
var each = function() {...};
var waitForAll = true;

// This works...
$(selector).waitForImages(finished, each, waitForAll);

// And now so does this...
$(selector).waitForImages({
  finished: finished,
  each: each,
  waitForAll: waitForAll
});
```

Sorry, I couldn't figure out how to write a test case for this, so have just committed the source and dist files.