Add implicit operator float(NDArray nd) for scalar value.

Add Single type string format.
Simplify element index for Data.

Author: Oceania2018

src/NumSharp.Core/Casting/Implicit/NdArray.Implicit.ValueTypes.cs

@@ -30,6 +30,14 @@ namespace NumSharp.Core
 {
     public partial class NDArray
     {
+        public static implicit operator float(NDArray nd)
+        {
+            if (nd.ndim > 0)
+                throw new IncorrectShapeException();
+
+            return nd.Data<float>(0);
+        }
+
         public static implicit operator NDArray(float d)
         {
             var ndArray = new NDArray(typeof(float), new int[0]);

src/NumSharp.Core/Casting/NdArray.ToString.cs

@@ -21,6 +21,9 @@ public override string ToString()
                     case "Int32":
                         output = Data<int>()[0].ToString();
                         break;
+                    case "Single":
+                        output = Data<float>()[0].ToString();
+                        break;
                     case "Double":
                         output = Data<double>()[0].ToString();
                         break;

src/NumSharp.Core/NdArray.cs

@@ -66,6 +66,8 @@ public partial class NDArray : ICloneable
         /// <returns></returns>
         public T[] Data<T>() => Storage.GetData<T>();
 
+        public T Data<T>(int index) => Storage.GetData<T>()[index];
+
         public Array Data() => Storage.GetData(dtype);
 
         /// <summary>