added a few new functions and refactored
Renamed, according to golang convension.
added a fake handler that will always return successfully, and will serve as th head node in our linked list of handlers. Also added a package level variable that maps file extensions to commands to invoke their approperate interpretter.
removed old files that were renamed into the go convension, and shredded a lot of useless code in ShellHandler file, which was made obsolete by my better understanding of our approach.