Updated the matrix exponentiation approach of finding nth fibonacci.

- Removed some extra spaces
- Added the complexity of bruteforce algorithm
- Removed unused function called zerro()
- Added some docktest based on request

Author: mahbubcseju

matrix/nth_fibonacci_using_matrix_exponentiation.py

@@ -12,7 +12,6 @@
 ->  [f(n),f(n-1)] = [[1,1],[1,0]]^(n-1) * [f(1),f(0)]
 So we just need the n times multiplication of  the matrix [1,1],[1,0]].
 We can decrease the n times multiplication by following  the divide and conquer approach.
-
 """
 from __future__ import print_function
 
@@ -38,7 +37,7 @@ def identity(n):
 def nth_fibonacci(n):
     """
     >>> nth_fibonacci(100)
-    354224848179261915075L
+    354224848179261915075
     >>> nth_fibonacci(-100)
     -100
     """