Adds method rand() to global objects Int and Float and qsort() to List.

Qsort() uses quicksort instead of bubble sort which is much more
efficient with bigger lists.

Also adds two examples.
It would be better (and safer when this function is called recursively) to return a `bool` which informs whether the operation was successfull or not, rather than taking a reference to boolean. (Which is not tested in later calls of this function.)