C# Bindings - Prompt formatting (#712)

* Added support for custom prompt formatting

* more docs added

* bump version

gpt4all-bindings/csharp/Gpt4All/Model/IGpt4AllModel.cs

@@ -2,4 +2,9 @@
 
 public interface IGpt4AllModel : ITextPrediction, IDisposable
 {
+    /// <summary>
+    /// The prompt formatter used to format the prompt before
+    /// feeding it to the model, if null no transformation is applied
+    /// </summary>
+    IPromptFormatter? PromptFormatter { get; set; }
 }