ADD: get_cached_only for FunctionCache. Therefore removed the optional parameter 'return_cached_only' in get.
UPD: moved partial import to FunctionCache. The caller can now just set the name of the function and provide the parameters. No import of functool on the the callers site.
UPD: moved item implementations into package 'items'
UPD: items are now real container to hold only data.
UPD: restructure of the tests
UPD: complete rework of the items
ADD: iso8601 - date only
UPD: complete new ISO 8601 parser which uses date, datetime and timedelta classes.
UPD: finished all basic information and convertion of items
UPD: seems to work
UPD: moved impl to system
UPD: cleaned up logging
ADD: some simple tests to see if logging works