fix a bug that 'replace' merge strategy (value: 0) was evaluated as False and cause an 'invalid strategy' error, and change default merging strategy
fix a bug that 'replace' merge strategy (value: 0) was evaluated as False and cause an 'invalid strategy' error, and change default merging strategy

ssato/python-anyconfig,pmquang/python-anyconfig,pmquang/python-anyconfig,ssato/python-anyconfig