feat(rust): add vowel count kata

rust/tests/7_vowel_count.rs

@@ -0,0 +1,8 @@
+fn get_count(string: &str) -> usize {
+    string.matches(&['a', 'e', 'i', 'o', 'u'][..]).count()
+}
+
+#[test]
+fn my_tests() {
+    assert_eq!(get_count("abracadabra"), 5);
+}