* Introduction of PeersetHandle
* integrate PeersetHandle with the rest of the codebase
* fix compilation errors
* more tests for peerset, fixed overwriting bug in add_reserved_peer
* Slots data structure and bugfixes for peerset
* bend to pressure
* updated lru-cache to 0.1.2 and updated linked-hash-map to 0.5.2
* peerset discovered list is now a LinkedHashMap
* fix review suggestions
* split back Peerset and PeersetHandle
* test for Peerset::discovered
* applied review suggestions
* fixes to peerset::incoming
* peerset disconnects are all instantaneous
* instantaneous drop in peerset finished
* Peerset::set_reserved_only can also reconnect nodes
* Peerset scores cache uses lru-cache
* remove redundant function call and comment from Peerset::on_set_reserved_only
* add_peer returns SlotState enum
* apply review suggestions
* is_reserved -> is_connected_and_reserved