Adds helper overloads for Markup calls without args

Without specific overloads without the args string.format will get called even if it's not needed. 

This closes #309

src/Spectre.Console/AnsiConsole.Markup.cs

@@ -7,6 +7,15 @@ namespace Spectre.Console
     /// </summary>
     public static partial class AnsiConsole
     {
+        /// <summary>
+        /// Writes the specified markup to the console.
+        /// </summary>
+        /// <param name="value">The value to write.</param>
+        public static void Markup(string value)
+        {
+            Console.Markup(value);
+        }
+
         /// <summary>
         /// Writes the specified markup to the console.
         /// </summary>
@@ -28,6 +37,15 @@ namespace Spectre.Console
             Console.Markup(provider, format, args);
         }
 
+        /// <summary>
+        /// Writes the specified markup, followed by the current line terminator, to the console.
+        /// </summary>
+        /// <param name="value">The value to write.</param>
+        public static void MarkupLine(string value)
+        {
+            Console.MarkupLine(value);
+        }
+
         /// <summary>
         /// Writes the specified markup, followed by the current line terminator, to the console.
         /// </summary>