add Feed, FeedList class which are interable
change test code for iterable FeedList
move convert_xx_outline function into `FeedList`
FeedList can have same Feed on multi category
Feed's type is 'rss' -> 'feed'. now AlreadyExist raises corectly.
fix some errors
Category also must have text attribute
schema.py changed. so we can have OutlineElement in OutlineElement
FeedList has more information with OPML format.
changed test code for FeedList.window_left, etc.
datetime is not support timezone, so use libearth.tz
fix bug when FeedList.save_file saves window_xxx as "None" string
remove unused import and variables
from . import tz -> from .tz import now
added encoder, decoder to date_created and date_modified
add ownerId element, fix time format
text attribute is required, pep8
added Integer, Rfc822 codec
encoder, decoder moved to Codec
added Boolean Codec, other special attributes
change arguments of Boolean codec