Add interactive prompts for selecting values

* Adds SelectionPrompt
* Adds MultiSelectionPrompt

Closes #210

docs/input/prompts/multiselection.md

@@ -0,0 +1,31 @@
+Title: Multi Selection
+Order: 3
+---
+
+The `MultiSelectionPrompt` can be used when you want the user to select
+one or many items from a provided list.
+
+<img src="../assets/images/multiselection.gif" style="width: 100%;" />
+
+# Usage
+
+```csharp
+// Ask for the user's favorite fruits
+var fruits = AnsiConsole.Prompt(
+    new MultiSelectionPrompt<string>()
+        .Title("What are your [green]favorite fruits[/]?")
+        .NotRequired() // Not required to have a favorite fruit
+        .PageSize(10)
+        .AddChoice("Apple")
+        .AddChoices(new[] {
+            "Apricot", "Avocado", 
+            "Banana", "Blackcurrant", "Blueberry",
+            "Cherry", "Cloudberry", "Cocunut",
+        }));
+
+// Write the selected fruits to the terminal
+foreach (string fruit in fruits) 
+{
+    AnsiConsole.WriteLine(fruit);
+}
+```