Add constructor ArrayString::from_byte_string(b"abc")

This is an alternative constructor that never has capacity errors.
Unfortunately the error case is invalid UTF-8!

tests/tests.rs

@@ -346,6 +346,14 @@ fn test_string_from() {
     assert_eq!(u.len(), text.len());
 }
 
+#[test]
+fn test_string_from_bytes() {
+    let text = "hello world";
+    let u = ArrayString::from_byte_string(b"hello world").unwrap();
+    assert_eq!(&u, text);
+    assert_eq!(u.len(), text.len());
+}
+
 #[test]
 fn test_string_clone() {
     let text = "hi";