Add count sort to sorting.py (Let's include everything in this repo and make it best online source for learning python)

`def count_sort(input_arr):
    M=max(input_arr)
    count_arr=[0]*(M+1)
    for num in input_arr:
        count_arr[num]+=1
    for i in range(1,M+1):
        count_arr[i]+=count_arr[i-1]
    out_arr=[0]*len(input_arr)
    for i in range(len(input_arr)-1,-1,-1):
        out_arr[count_arr[input_arr[i]]-1]=input_arr[i]
        count_arr[input_arr[i]]-=1
    return out_arr
`