Parent os no longer mandatory parameter to leaf_node (as it can be set also later).
Added note about how to handle IDNA in phase 1 - just use GNU libidn's idn tool.
Some rewriting of the cache code. Now it can use _either_ timeouts, or maximum number of items.
Refactored cache so that time_callback in and of itself is optional and keeps track of calls by default. Now seems to be fairly useful cache abstraction with both time- and item count based LRU/TTL semantics available.