Add support for markdown tables

Closes #85

* Split Border into BoxBorder and TableBorder
* Change how different table parts are composed
* Add markdown table border

src/Spectre.Console/Internal/Extensions/StringExtensions.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using Spectre.Console.Rendering;
 
@@ -80,27 +81,24 @@ namespace Spectre.Console.Internal
             return result.ToArray();
         }
 
-        // https://andrewlock.net/why-is-string-gethashcode-different-each-time-i-run-my-program-in-net-core/
-        public static int GetDeterministicHashCode(this string str)
+        public static string Multiply(this string text, int count)
         {
-            unchecked
+            if (text is null)
             {
-                var hash1 = (5381 << 16) + 5381;
-                var hash2 = hash1;
-
-                for (var i = 0; i < str.Length; i += 2)
-                {
-                    hash1 = ((hash1 << 5) + hash1) ^ str[i];
-                    if (i == str.Length - 1)
-                    {
-                        break;
-                    }
-
-                    hash2 = ((hash2 << 5) + hash2) ^ str[i + 1];
-                }
-
-                return hash1 + (hash2 * 1566083941);
+                throw new ArgumentNullException(nameof(text));
             }
+
+            if (count <= 0)
+            {
+                return string.Empty;
+            }
+
+            if (count == 1)
+            {
+                return text;
+            }
+
+            return string.Concat(Enumerable.Repeat(text, count));
         }
     }
 }