Added np.newaxis (not supported yet)

Author: Nucs

src/NumSharp.Core/APIs/np.cs

@@ -10,6 +10,12 @@ public static partial class np
     {
         public static BackendType BackendEngine { get; set; }
 
+        /// <summary>
+        ///     A convenient alias for None, useful for indexing arrays.
+        /// </summary>
+        /// <remarks>https://docs.scipy.org/doc/numpy-1.17.0/reference/arrays.indexing.html<br></br><br></br>https://stackoverflow.com/questions/42190783/what-does-three-dots-in-python-mean-when-indexing-what-looks-like-a-number</remarks>
+        public static readonly Slice newaxis = new Slice(null, null, 1) {IsNewAxis = true};
+
         // https://docs.scipy.org/doc/numpy-1.16.0/user/basics.types.html
         public static readonly Type bool_ = typeof(bool);
         public static readonly Type bool8 = bool_;

src/NumSharp.Core/Backends/Unmanaged/UnmanagedStorage.Slicing.cs

@@ -20,9 +20,12 @@ public UnmanagedStorage GetView(params Slice[] slices)
                 throw new ArgumentNullException(nameof(slices));
 
             foreach (var slice in slices)
+            {
                 if (slice.IsEllipsis)
                     throw new NotSupportedException("Ellipsis slicing '...' is not supported by NumSharp.");
-
+                if (slice.IsNewAxis)
+                    throw new NotSupportedException("np.newaxis slicing '...' is not supported by NumSharp. Consider calling np.expand_dims after performing slicing");
+            }
             //handle memory slice if possible
             if (!_shape.IsSliced)
             {