fixed %f formatting issues in datetime.strptime and datetime.strftime

strptime acts diffrently depending on module it is called from (dateime
vs. time)
added very basic test_datetime.py
fixed cp34706 and cp32215
bug fix and changes for [date]time.strptime

fixed cp30047, invalid format/input combinations are not silently converted
Merge pull request #166 from paweljasinski/cp34706

fixed %f formatting issues in datetime.strptime and datetime.strftime