This method will publish a private asset (file or directory)
and gets the URL to the asset. Note, if the asset refers to
a directory, all contents under that directory will be published.
Also note, it is recommended that you supply a class name as the second
parameter to the method (e.g. publishAsset($assetPath,__CLASS__) ).
By doing so, you avoid the issue that child classes may not work properly
because the asset path will be relative to the directory containing the child class file.