make org-e-caldav-event-to-headline remove the sync property if it is nil
reset state on remote error or conflict so syncing again works
make event-to-ical return a complete calendar resource
show conflicts which happened during the sync in an extra buffer/window
set-state doesn't need to be passed the previous state. it's managing it.
properly prefix org-e-caldav even abstract org-element functions
Add debug messages to functions, which change stuff.
load and write state from file during a sync cycle.
better comments and function ordering (no programmatic changes)
minimal cleanup in set-state
more reordering
small fix to property-drawer creation
improve doku and debug print.
move org-element-copy to be in front of merge-conflict
small fixes
check more thoroughly if updates are necessary

don't update if remote and local state are already identical and don't
update locally if nothing changed.
add final message
use assq instead of assoc where applicable
on a resolved conflict the :sync flag needs still to be removed
improve doku