Changed method signature to use interface List instead of implentation L...

Hello jRedditors! = ] Just getting started using jReddit for a project and noticed a little inconsistency in your API that I wanted to smooth out:

Changed method signature return type to use interface List instead of implementation LinkedList. Also removed JavaDoc mention of linked list to remove implementation from API documentation. This is to create a more generic API, and to be more consistent with the rest of the API that uses the interface description listed above.