Some minor improvements
added methode to exchange elements in MultiLists
renaming

- MultiList -> BaseList
- MultisSortrer -> BaseSorter
added unit test for classes that implement Sorter interface

tested methods: sort(), validate(), run()
added unit test for classes that implement SortList interface

tested methods: clone(), equals(), isSorted()
Merge pull request #5 from Pennham/penn-dev

Unit tests added