Added custom prompt handler (thanks walljm!)

Merged from tonerdo/readline#62

Author: AptiviCEO

README.md

@@ -72,6 +72,19 @@ _Note: The `(prompt>)` is  optional_
 string input = ReadLine.Read("(prompt)> ");
 ```
 
+#### Read input with default
+
+```csharp
+string input = ReadLine.Read("(prompt)> ", "default");
+```
+
+#### Read input with custom prompt handler
+
+```csharp
+ReadLine.WritePrompt = (prompt) => Console.Write($">> {prompt}");
+string input = ReadLine.Read("(prompt)> ", "default");
+```
+
 #### Read password
 
 ```csharp

src/ReadLine/ReadLine.cs

@@ -47,6 +47,11 @@ public static class ReadLine
         /// </summary>
         public static IAutoCompleteHandler AutoCompletionHandler { private get; set; }
 
+        /// <summary>
+        /// The prompt writing handler.
+        /// </summary>
+        public static Action<string> WritePrompt { private get; set; } = (prompt) => Console.Write(prompt);
+
         private static readonly List<string> _history = new List<string>();
 
         /// <summary>
@@ -83,7 +88,7 @@ public static void SetHistory(List<string> history)
         public static string Read(string prompt = "", string defaultText = "")
         {
             // Prepare the prompt
-            Console.Write(prompt);
+            WritePrompt.Invoke(prompt);
             KeyHandler keyHandler = new KeyHandler(new ConsoleWrapper(), _history, AutoCompletionHandler);
 
             // Get the written text
@@ -114,7 +119,7 @@ public static string Read(string prompt = "", string defaultText = "")
         public static string ReadPassword(string prompt = "", char mask = default)
         {
             // Prepare the prompt
-            Console.Write(prompt);
+            WritePrompt.Invoke(prompt);
             KeyHandler keyHandler = new KeyHandler(new ConsoleWrapper() { PasswordMode = true, PasswordMaskChar = mask }, null, null);
 
             // Get the written text

test/ReadLine.Demo/Program.cs

@@ -50,16 +50,22 @@ public static void Main()
             Console.WriteLine(input);
 
             // Enter the prompt with default
-            string input2 = ReadLine.Read("(prompt2)> [def] ", "def");
-            Console.WriteLine(input2);
+            input = ReadLine.Read("(prompt2)> [def] ", "def");
+            Console.WriteLine(input);
+
+            // Enter the prompt with custom prompt handler
+            ReadLine.WritePrompt = (prompt) => Console.Write($">> {prompt}");
+            input = ReadLine.Read("(prompt3)> ");
+            Console.WriteLine(input);
+            ReadLine.WritePrompt = (prompt) => Console.Write(prompt);
 
             // Enter the masked prompt
-            string input3 = ReadLine.ReadPassword("Enter Password> ");
-            Console.WriteLine(input3);
+            input = ReadLine.ReadPassword("Enter Password> ");
+            Console.WriteLine(input);
 
             // Enter the masked prompt with password mask
-            string input4 = ReadLine.ReadPassword("Enter Password> ", '*');
-            Console.WriteLine(input4);
+            input = ReadLine.ReadPassword("Enter Password> ", '*');
+            Console.WriteLine(input);
         }
     }
 }