Removed spaces from top-level directory names.

Spaces tend to cause annoyances in a Unix-style shell environment.
This change fixes that.

10_Blackjack/csharp/Prompt.cs

@@ -0,0 +1,58 @@
+using System;
+
+namespace Blackjack
+{
+    public static class Prompt
+    {
+        public static bool ForYesNo(string prompt)
+        {
+            while(true)
+            {
+                Console.Write("{0} ", prompt);
+                var input = Console.ReadLine();
+                if (input.StartsWith("y", StringComparison.InvariantCultureIgnoreCase))
+                    return true;
+                if (input.StartsWith("n", StringComparison.InvariantCultureIgnoreCase))
+                    return false;
+                WriteNotUnderstood();
+            }
+        }
+
+        public static int ForInteger(string prompt, int minimum = 1, int maximum = int.MaxValue)
+        {
+            while (true)
+            {
+                Console.Write("{0} ", prompt);
+                if (!int.TryParse(Console.ReadLine(), out var number))
+                    WriteNotUnderstood();
+                else if (number < minimum || number > maximum)
+                    Console.WriteLine("Sorry, I need a number between {0} and {1}.", minimum, maximum);
+                else
+                    return number;
+            }
+        }
+
+        public static string ForCommandCharacter(string prompt, string allowedCharacters)
+        {
+            while (true)
+            {
+                Console.Write("{0} ", prompt);
+                var input = Console.ReadLine();
+                if (input.Length > 0)
+                {
+                    var character = input.Substring(0, 1);
+                    var characterIndex = allowedCharacters.IndexOf(character, StringComparison.InvariantCultureIgnoreCase);
+                    if (characterIndex != -1)
+                        return allowedCharacters.Substring(characterIndex, 1);
+                }
+
+                Console.WriteLine("Type one of {0} please", String.Join(", ", allowedCharacters.ToCharArray()));
+            }
+        }
+
+        private static void WriteNotUnderstood()
+        {
+            Console.WriteLine("Sorry, I didn't understand.");
+        }
+    }
+}