Assignment name  : sort_list
Expected files   : sort_list.c
Allowed functions: 
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Write the following function:

t_list  *sort_list(t_list* lst, int (*cmp)(int, int));

This function must sort the list given as a parameter, using the function 
pointer cmp to select the order to apply, and returns a pointer to the 
first element of the sorted list.

Duplications must remain.

Inputs will always be consistent.

You must use the type t_list described in the file list.h 
that is provided to you. You must include that file 
(#include "list.h"), but you must not turn it in. We will use our own 
to compile your assignment.

Functions passed as cmp will always return a value different from 
0 if a and b are in the right order, 0 otherwise.

For example, the following function used as cmp will sort the list 
in ascending order:

int ascending(int a, int b)
{
    return (a <= b);
}