simplifyPath() "fits" better to Path class conceptually. It handles
paths, not lists them. Also this way we get rid of few unneeded
dependencies to FileLister class.
Improve the system used to have separate versions of code of FileLister for
Win32 and Linux. New idea is to have Base FileLister class implementing
common code and then derived classes for Win32 and Linux specific code.
FileLister is not anymore a static class. Instead we use singleton of
derived class.