Added matrix exponentiation approach for finding fibonacci number. (#1042)

* Added matrix exponentiation approach for finding fibonacci number.

* Implemented the way of finding nth fibonacci.
* Complexity is about O(log(n)*8)

* 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

* 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

* Tighten up main() and add comments on performance