Parse itemids and coords, save to $tiles array

Patch for parsing item IDs on tiles. Can used to parse the layout of a map.

```php
$map = new OTS_OTBMFile();
$map->loadFile('gm-isle.otbm');
$output = array(
  'name' => 'gm-isle.otbm',
  'desc' => $map->getDescription(),
  'width' => $map->getWidth(),
  'height' => $map->getHeight(),
  'tiles' => $map->tiles,
);
```