Implement NavigableMap with O(1) snapshots

[rovarga]

The TrieMap is an implementation of a Ctrie. This means its iteration order is defined in terms of hashCode() of keys of stored mappings -- essentially an equivalent of a ConcurrentHashMap.

Explore the possibility of implementing a ConcurrentMap + NavigableMap with O(1) snapshots. This should follow the same internal organization as TrieMap has. One notable difference is the need to pass around Comparators and using them to locate and organize the entries. For the equivalent of CNode, we should be able to use a suitably-sized array sorted using Arrays.sort().