feat(KvStore): new, get, set, remove functions implementation

- Added a new test for empty key

tests/tests.rs

@@ -153,3 +153,11 @@ fn remove_key() {
     store.remove("key1".to_owned());
     assert_eq!(store.get("key1".to_owned()), None);
 }
+
+#[test]
+fn get_empty_key() {
+    let mut store = KvStore::new();
+
+    store.set("".to_owned(), "value1".to_owned());
+    assert_eq!(store.get("".to_owned()), Some("value1".to_owned()));
+}