Add parameterless Clear method for IAnsiConsole

Closes #338

src/Spectre.Console/AnsiConsole.cs

@@ -66,5 +66,13 @@ namespace Spectre.Console
             var factory = new AnsiConsoleFactory();
             return factory.Create(settings);
         }
+
+        /// <summary>
+        /// Clears the console.
+        /// </summary>
+        public static void Clear()
+        {
+            Console.Clear();
+        }
     }
 }

src/Spectre.Console/Extensions/AnsiConsoleExtensions.cs

@@ -17,6 +17,20 @@ namespace Spectre.Console
             return new Recorder(console);
         }
 
+        /// <summary>
+        /// Clears the console.
+        /// </summary>
+        /// <param name="console">The console to clear.</param>
+        public static void Clear(this IAnsiConsole console)
+        {
+            if (console is null)
+            {
+                throw new ArgumentNullException(nameof(console));
+            }
+
+            console.Clear(true);
+        }
+
         /// <summary>
         /// Writes the specified string value to the console.
         /// </summary>