Add bottom border to ToString output

Update README
Use approval testing pattern for ToString()

Fig.Core/CompositeSettingsDictionary.cs

@@ -83,6 +83,8 @@ public string AsString()
                 }
             }
 
+            sb.AppendLine("-".PadRight(colWidths.Sum(w => w) + 7, '-'));
+
             return sb.ToString();
         }
 

Fig.Tests/DictionaryTests.cs

@@ -98,14 +98,13 @@ public void AsString()
 
             Console.WriteLine(toString);
 
-            Assert.AreEqual(toString, cd.AsString());
-
-            Assert.True(toString.Contains("- Layer 0 -"));
-            Assert.True(toString.Contains("- Layer 1 -"));
-            Assert.True(toString.Contains("| a "));
-            Assert.True(toString.Contains("| b "));
-            Assert.True(toString.Contains("| c:prod "));
-            Assert.True(toString.Contains("| d "));
+            var expected =   "-------------------- Layer 0 ----------------------\n"
+                           + "| a                      | b                      |\n"
+                           + "-------------------- Layer 1 ----------------------\n"
+                           + "| c:prod                 | d                      |\n"
+                           + "---------------------------------------------------\n";
+
+            Assert.AreEqual(expected, toString);
         }
 
         [Test]

README.md

@@ -279,6 +279,7 @@ Install-Package Fig.AppSettingsJson
 ## What do I have?
 `Settings.ToString()` is your friend. It will return a plain-text formatted table
 with keys and values of each layer:
+
 ```
 -------------------- Layer 0 ----------------------
 | Network.ip:TEST        | 127.0.0.1              |