new timezone creation

fix #120 and hopefully #123 

merging this, even if it is not perfect yet as it is better than before anyway

tz._tzinfos is indead a dict, have a look at `DstTzInfo` in pytz
(*tzinfo.py*). What difference would the order make?

Quoting Markus Unterwaditzer (2014-10-28 16:39:16)
> > +    As this information is not provided by pytz at all, there is no
> > +    easy solution, we'd really need to ship another version of the OLSON DB.
> > +
> > +    """
> > +
> > +    # TODO last_date = None, recurring to infintiy
> > +    # TODO use RDATE, not seperate subcomponents
> > +
> > +    first_date = datetime.datetime.today() if not first_date else first_date
> > +    last_date = datetime.datetime.today() if not last_date else last_date
> > +    timezone = icalendar.Timezone()
> > +    timezone.add('TZID', tz)
> > +
> > +    dst = {one[2]: 'DST' in two.__repr__() for one, two in tz._tzinfos.iteritems()}
> > +    # let's hope those transition times are alway ordered (but it does look
> > +    # like it)
> 
> I meant ``tz._tzinfos``. But i didn't manage to find this internal parameter in either stdlib datetime or pytz. Where did you get it?
> 
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