Right now we ignore already parsed entries and store the information
at runtime, but it will not survive a restart. This patch adds storage
functionality storing pickled file into default config folder when
feed has `published_parsed` support.
* process only last 20 available entries to avoid bombing event
bus when parsing huge feeds
* trigger first update only when HA has completed startup,
allowing components to complete subscriptions to feedreader
events
* quote url in logs for better readability
* bugfix: ignore not existing property in feedreader item
* add info and debug data
* split logic in smaller and hopefully easier to understand functions
Alexander Fortin
Fabian Affolter