Fix convert_datetime_to_utc() test.

The test had two flaws:
 1. The actual date was different (4/1 vs 1/1)
 2. The timezone usage was not correct (using the timezone as an
    argument of the datetime constructors won't work with timezones
    with daylight saving time according to documentation).
Fix usage of timezones in the documentation.

According to the pytz documentation, using the timezone as an argument
of the datetime constructors won't work with timezones with daylight
saving time, so let's be on the safe side and promote usage of the
localize() method of timezones.
Merge pull request #23 from nud/fix-tz-test

Fix convert_datetime_to_utc() test.
Minor updates - we're using pytest, not nosetests
Ensure we have the right 's' prefix for the SOAP elements.

Previously, we let ElementTree pick its own prefix, and it took 'ns0'.
Log request errors.

This is much needed when you get 500's, which usually come with an
explanation on why the request was not accepted.
Fix getting a calendar event list with Exchange 14.2.247.0

The SOAP query was returing the following error:

    The request failed schema validation: The 'EndDate' attribute is
    invalid - The value '2014-10-28' is invalid according to its
    datatype 'http://www.w3.org/2001/XMLSchema:dateTime' - The string
    '2014-10-28' is not a valid XsdDateTime value.

The fix is simply to use the DATETIME format instead of the DATE format,
as advised in the MSDN page of the CalendarView element.

http://msdn.microsoft.com/en-us/library/office/aa564515%28v=exchg.140%29.aspx