Given a name, turn that name into a perfect square matrix (nested array with the amount of arrays equivalent to the length of each array). 
You will need to add periods (`.`) to the end of the name if necessary, to turn it into a matrix. 
If the name has a length of 0, return `"name must be at least one letter"`
## Examples
"Bill" ==> [ ["B", "i"],
             ["l", "l"] ]
"Frank" ==> [ ["F", "r", "a"],
              ["n", "k", "."],
              [".", ".", "."] ]
from math import ceil

def matrixfy(s):
    if not s: return "name must be at least one letter"
    x  = ceil(len(s)**.5)
    it = iter(s.ljust(x*x,'.'))
    return [ [next(it) for _ in range(x)] for _ in range(x)]
from math import ceil

def matrixfy(s):
    if not s: return "name must be at least one letter"
    x  = ceil(len(s)**.5)
    it = iter(s.ljust(x*x,'.'))
    return [ [next(it) for _ in range(x)] for _ in range(x)]