File Tracker implementation with polling.

@bsoetaer 
It would be a lot of work to use INotify without using any external libraries, and since Miller hinted in class that polling would be OK for this part, I figured that would be the best way to go.

For part 2, how much are you implementing in C?  I think that a precise sleep method should be enough - then we can reuse it in part 3.
Also if the block is intended to print something using puts or print I believe this won't work as when I put a printout inside a thread, the thread is actually terminated by the printout line and then the printout line is only printed out when a join happens.