[doc] Add documentation for .notice() and the notice parameter in .reply()
[core] Check python version earlier, also check for 3.3

Since argparse is not present in Python 2.6 and Python 3.2, we can't wait
until after parsing the args to show the "python version too low" error.

This commit fixes this by checking the python version before parsing the args.
This commit also makes sure we display a meaningful error message
for people who run Python 3 older than 3.3.