Added the logger class and its unittest

Added the singleton_meta_class used in the logger
Added comments to constant module
Merge https://github.com/edson-gonzales/Sudoku-A2

Conflicts:
	src/constant.py
Corrected misspelling in some Classes

Updated the import in some unittest in order to execute the code coverage
Added some comments to methods
Added the test_suite in order to execute all the unittest and calculate the code coverage
Updated the Logger and Singleton meta class according to code review

Updated the variable and method name in the logger unittest