trie: add get function

lib/util/trie.js

@@ -160,6 +160,19 @@ export const suggest = trie => key => maxSuggestions => {
   return __suggest(trie, "", key, maxSuggestions);
 }
 
+export const get = trie => key => {
+  if (key === '') {
+    return trie.value;
+  }
+  const [pos] = binarySearch(trie.children, key);
+  if (pos < trie.children.length) {
+    const [haveKey, haveChildNode] = trie.children[pos];
+    if (key.startsWith(haveKey)) {
+      return get(haveChildNode)(key.slice(haveKey.length));
+    }
+  }
+}
+
 const __suggest = (trie, path, remaining, maxSuggestions) => {
   if (maxSuggestions === 0) {
     return [];