WIP
WIP
WIP: operator[]
WIP
WIP: TrieTraits and TrieBase
WIP: max_size
WIP: emplace
WIP: erase children
WIP: Makefile.am
WIP: clear
WIP

- merge node, base, and trie classes
- all nodes now have pointer to its parent
- emplace -> emplaceValue
WIP: emplaceChild
WIP
WIP
WIP: forward traversal
WIP: down, key digit
WIP: down, key iterator
WIP: down, key string
WIP: up
WIP: traverser forward subtree