Disable Json.Net reference handling for SendGrid objects

Author: sepptruetsch

src/SendGrid/Helpers/Mail/Model/ASM.cs

@@ -11,6 +11,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// An object allowing you to specify how to handle unsubscribes.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class ASM
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/Attachment.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// Gets or sets an array of objects in which you can specify any attachments you want to include.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class Attachment
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/BCCSettings.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// Gets or sets the address specified in the mail_settings.bcc object will receive a blind carbon copy (BCC) of the very first personalization defined in the personalizations array.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class BCCSettings
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/BypassListManagement.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// Allows you to bypass all unsubscribe groups and suppressions to ensure that the email is delivered to every single recipient. This should only be used in emergencies when it is absolutely necessary that every recipient receives your email. Ex: outage emails, or forgot password emails.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class BypassListManagement
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/ClickTracking.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// Allows you to track whether a recipient clicked a link in your email.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class ClickTracking
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/Content.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// Specifies the content of your email. You can include multiple mime types of content, but you must specify at least one. To include more than one mime type, simply add another object to the array containing the type and value parameters. If included, text/plain and text/html must be the first indices of the array in this order. If you choose to include the text/plain or text/html mime types, they must be the first indices of the content array in the order text/plain, text/html.*Content is NOT mandatory if you using a transactional template and have defined the template_id in the Request
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class Content
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/EmailAddress.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// An email object containing the email address and name of the sender or recipient.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class EmailAddress
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/FooterSettings.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// The default footer that you would like appended to the bottom of every email.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class FooterSettings
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/Ganalytics.cs

@@ -10,6 +10,7 @@ namespace SendGrid.Helpers.Mail
     /// <summary>
     /// Allows you to enable tracking provided by Google Analytics.
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class Ganalytics
     {
         /// <summary>

src/SendGrid/Helpers/Mail/Model/HtmlContent.cs

@@ -5,9 +5,12 @@
 
 namespace SendGrid.Helpers.Mail.Model
 {
+    using Newtonsoft.Json;
+
     /// <summary>
     /// Helper class for plain html mime types
     /// </summary>
+    [JsonObject(IsReference = false)]
     public class HtmlContent : Content
     {
         /// <summary>