added basic unit tests

examples/benchmark.rs

@@ -47,6 +47,7 @@ fn main() {
     for key in keys {
         let word = &key.into_char_slice()[..];
         let results = trie.fuzzy_search::<DamerauLevenshteinDistanceCalculator>(word, 6);
+        println!("needle: {}", key);
         for result in results {
             let word: String = trie.lineal_descendant(result.word).into_iter().collect();
             println!("distance: {}, wordkey: {}", result.distance, word);