added topics for prime-factors, resolves #833
added topics for prime-factors, resolves #833

jmluy/xpython,jmluy/xpython,smalley/python,pheanex/xpython,behrtam/xpython,exercism/python,mweb/python,smalley/python,N-Parsons/exercism-python,N-Parsons/exercism-python,pheanex/xpython,exercism/xpython,behrtam/xpython,mweb/python,exercism/python,exercism/xpython