ENDIAN- and TODAY-classes

ENDIAN is now an iterable object with a set-method to change the
order-tuple to iter over. set accepts an string as argument which is
checked for matching an endian-key (little, big or medium).

TODAY is a datetime.date that defaults to datetime.date.today(), which
also has a set-method to change the date of TODAY. Tooks a
datetime.date-instance as argument.

TODO: write docstrings...
initializing and setting TODAY like datetime.date
ENDIAN as subclass of list for a mutable self
TODAY: imutable but reconfigurable obj

Because TODAY inherit from datetime.date it wasn't mutable at all. So
the only option changing TODAY-obj was recreating it.

To have a imutable but reconfigureable TODAY-obj (TODAY.set()) with an
unbroken identity, I decided to 'rebuilt' a simple date instead of
inheriting from datetime.date. To have a comparable consistence, TODAY
defines a property dateobj, which is a 'real' datetime.date-obj. Year-,
month- and day-property just return the accordant dateobj-attributes.
That way successfully initializing (and setting) TODAY depends on
successfully initializing datetime.date.
For further options of datetime.date-objs one can use the
dateobj-attr directly.
ENDIAN: imutable but reconfigureable

switched back to the earlier version of the ENDIAN-class. Because it
harmonizes with the imutable-but-reconfigurable-concept.
Inheriting from list, TODAY were mutable...
Now it is a class on its own imitating an iterable.
v0.5 setEndian and setToday deprecated

setEndian and setToday are deprecated but still available for
backwars-compatibility.

Add Docstrings to ENDIAN and TODAY; add Change-Notes to README.rst