Added Product field to license

src/Portable.Licensing.Tests/LicenseValidationTests.cs

@@ -100,7 +100,7 @@ public void Can_Validate_Invalid_Signature()
         [Test]
         public void Can_Validate_Expired_ExpirationDate()
         {
-            var publicKey = "";
+            //var publicKey = "";
             var licenseData = @"<License>
                                   <Id>77d4c193-6088-4c64-9663-ed7398ae8c1a</Id>
                                   <Type>Trial</Type>

src/Portable.Licensing/ILicenseBuilder.cs

@@ -32,7 +32,14 @@ namespace Portable.Licensing
     /// Fluent api to create and sign a new <see cref="License"/>. 
     /// </summary>
     public interface ILicenseBuilder : IFluentInterface
-    {
+    {
+        /// <summary>
+        /// Sets the product name of the <see cref="License"/>.
+        /// </summary>
+        /// <param name="product">The product name of the <see cref="License"/>.</param>
+        /// <returns>The <see cref="ILicenseBuilder"/>.</returns>
+        ILicenseBuilder WithProduct(string product);
+
         /// <summary>
         /// Sets the unique identifier of the <see cref="License"/>.
         /// </summary>

src/Portable.Licensing/License.cs

@@ -69,6 +69,15 @@ public Guid Id
         {
             get { return new Guid(GetTag("Id") ?? Guid.Empty.ToString()); }
             set { if (!IsSigned) SetTag("Id", value.ToString()); }
+        }
+
+        /// <summary>
+        /// Gets or sets the product name this <see cref="License"/> applies to.
+        /// </summary>
+        public String Product
+        {
+            get { return GetTag("Product") ?? ""; }
+            set { if (!IsSigned) SetTag("Product", value); }
         }
 
         /// <summary>
@@ -167,7 +176,7 @@ public LicenseAttributes AdditionalAttributes
         /// <summary>
         /// Gets or sets the expiration date of this <see cref="License"/>.
         /// Use this property to set the expiration date for a trial license
-        /// or the expiration of support & subscription updates for a standard license.
+        /// or the expiration of support and subscription updates for a standard license.
         /// </summary>
         public DateTime Expiration
         {

src/Portable.Licensing/LicenseBuilder.cs

@@ -42,6 +42,18 @@ internal class LicenseBuilder : ILicenseBuilder
         public LicenseBuilder()
         {
             license = new License();
+        }
+
+
+        /// <summary>
+        /// Sets the product name of the <see cref="License"/>.
+        /// </summary>
+        /// <param name="product">The product name of the <see cref="License"/>.</param>
+        /// <returns>The <see cref="ILicenseBuilder"/>.</returns>
+        public ILicenseBuilder WithProduct(string product)
+        {
+            license.Product = product;
+            return this;
         }
 
         /// <summary>