Add additional array -> array view conversions

It is best to be "complete" with implementations when possible, since
it can always be a breaking change to add it later.

As shown in the test change in this commit, this is a minor type
inference breakage due to `ArrayView::from(&[])` being ambiguous.

Empty array views should be relatively rare - and one can use
`ArrayView1` or other means to disambiguate.

src/arraytraits.rs

@@ -323,7 +323,18 @@ where
     }
 }
 
-/// Implementation of ArrayView2::from(&S) where S is a slice to a 2D array
+/// Implementation of ArrayView2::from(&[[A; N]; M])
+///
+/// **Panics** if the product of non-zero axis lengths overflows `isize` (This can only occur if A
+/// is zero-sized because slices cannot contain more than `isize::MAX` number of bytes).
+impl<'a, A, const M: usize, const N: usize> From<&'a [[A; N]; M]> for ArrayView<'a, A, Ix2> {
+    /// Create a two-dimensional read-only array view of the data in `slice`
+    fn from(xs: &'a [[A; N]; M]) -> Self {
+        Self::from(&xs[..])
+    }
+}
+
+/// Implementation of ArrayView2::from(&[[A; N]])
 ///
 /// **Panics** if the product of non-zero axis lengths overflows `isize` (This can only occur if A
 /// is zero-sized because slices cannot contain more than `isize::MAX` number of bytes).
@@ -379,7 +390,18 @@ where
     }
 }
 
-/// Implementation of ArrayViewMut2::from(&S) where S is a slice to a 2D array
+/// Implementation of ArrayViewMut2::from(&mut [[A; N]; M])
+///
+/// **Panics** if the product of non-zero axis lengths overflows `isize` (This can only occur if A
+/// is zero-sized because slices cannot contain more than `isize::MAX` number of bytes).
+impl<'a, A, const M: usize, const N: usize> From<&'a mut [[A; N]; M]> for ArrayViewMut<'a, A, Ix2> {
+    /// Create a two-dimensional read-write array view of the data in `slice`
+    fn from(xs: &'a mut [[A; N]; M]) -> Self {
+        Self::from(&mut xs[..])
+    }
+}
+
+/// Implementation of ArrayViewMut2::from(&mut [[A; N]; M])
 ///
 /// **Panics** if the product of non-zero axis lengths overflows `isize` (This can only occur if A
 /// is zero-sized because slices cannot contain more than `isize::MAX` number of bytes).

tests/append.rs

@@ -339,8 +339,8 @@ fn test_append_zero_size() {
 
     {
         let mut a = Array::<i32, _>::zeros((0, 0));
-        a.append(Axis(1), ArrayView::from(&[]).into_shape((0, 1)).unwrap()).unwrap();
-        a.append(Axis(1), ArrayView::from(&[]).into_shape((0, 1)).unwrap()).unwrap();
+        a.append(Axis(1), ArrayView1::from(&[]).into_shape((0, 1)).unwrap()).unwrap();
+        a.append(Axis(1), ArrayView1::from(&[]).into_shape((0, 1)).unwrap()).unwrap();
         assert_eq!(a.len(), 0);
         assert_eq!(a.shape(), &[0, 2]);
     }