DatetimeTextRecord isn't handled correctly

Based on the datetime records I'm receiving from our .NET services and also based on the spec and examples at http://msdn.microsoft.com/en-us/library/cc219284.aspx, DatetimeTextRecord has the bit order wrong for the value and tz components.

I've added tests to the to_bytes() and parse() methods and my fix to the bit handling.

Best,
  Stefan