Merge pull request #20 from griera/master

Fixes some bugs detected after E1 final deliverable
Merge pull request #21 from griera/master

Adapts allocate_DIR() function and implements clone() system call. New a...
Merge pull request #22 from griera/master

Implements system calls sem_init and sem_destroy.
clone te els valors correctes a la pila
Test de clone
Test del clone