Add script as an option to the 'sum' function

Added script as the 4th parameter to the 'sum' function. Now, it is possible to perform more complexed operations on the sum function. For example, we can do the following:
Item::es()->aggregate('Value', function($q) {
$q->sum('', null, null, ['source' => 'doc.price.value * doc.quantity.value'])->groupBy('status');
})->get()->aggregations();

Prevent delete() from throwing 404 exception

v1.0.2

update readme file

Fixed a bug related to orWhere

v1.0.1

fixed a bug regarding to orWhere

First version

v1.0.0

add documentation for scroll