prime-factors: add parameters to exercise placeholder
prime-factors: add parameters to exercise placeholder

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