FIX: Add new_const() for const construction and revert new to old version

The new() function is significantly faster, it optimizes better at the
moment/in current rust. For this reason, provide a const fn constructor,
but not as the default `new`.

tests/tests.rs

@@ -718,19 +718,29 @@ fn allow_max_capacity_arrayvec_type() {
     let _v: ArrayVec<(), {usize::MAX}>;
 }
 
-#[should_panic(expected="index out of bounds")]
+#[should_panic(expected="largest supported capacity")]
 #[test]
 fn deny_max_capacity_arrayvec_value() {
     if mem::size_of::<usize>() <= mem::size_of::<u32>() {
-        panic!("This test does not work on this platform. 'index out of bounds'");
+        panic!("This test does not work on this platform. 'largest supported capacity'");
     }
     // this type is allowed to be used (but can't be constructed)
     let _v: ArrayVec<(), {usize::MAX}> = ArrayVec::new();
 }
 
+#[should_panic(expected="index out of bounds")]
+#[test]
+fn deny_max_capacity_arrayvec_value_const() {
+    if mem::size_of::<usize>() <= mem::size_of::<u32>() {
+        panic!("This test does not work on this platform. 'index out of bounds'");
+    }
+    // this type is allowed to be used (but can't be constructed)
+    let _v: ArrayVec<(), {usize::MAX}> = ArrayVec::new_const();
+}
+
 #[test]
 fn test_arrayvec_const_constructible() {
-    const OF_U8: ArrayVec<Vec<u8>, 10> = ArrayVec::new();
+    const OF_U8: ArrayVec<Vec<u8>, 10> = ArrayVec::new_const();
 
     let mut var = OF_U8;
     assert!(var.is_empty());
@@ -742,7 +752,7 @@ fn test_arrayvec_const_constructible() {
 
 #[test]
 fn test_arraystring_const_constructible() {
-    const AS: ArrayString<10> = ArrayString::new();
+    const AS: ArrayString<10> = ArrayString::new_const();
 
     let mut var = AS;
     assert!(var.is_empty());