Support date + time formats more flexibly

[kxrob]

Bugs / issues fixed:

• Many (locale) da-ti formats produced just a number before (days since 1900)

• PYVER > 3 is never True (before Python 4)

• less duplicate code regarding da-ti formats

• fix rounding issues like "07:30:54.9999999"

[PydPiper]

Hey @kxrob sorry for the delay, i just got a chance to look at this. I checked it out from my end. It looks great! Thank you for your contribution!