Add interactive prompts for selecting values

* Adds SelectionPrompt
* Adds MultiSelectionPrompt

Closes #210

docs/input/prompts/index.cshtml

@@ -0,0 +1,12 @@
+Title: Prompts
+Order: 5
+---
+
+<h1>Sections</h1>
+
+<ul>
+@foreach (IDocument child in OutputPages.GetChildrenOf(Document))
+{
+  <li>@Html.DocumentLink(child)</li>
+}
+</ul>

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);
+}
+```

docs/input/prompts/selection.md

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+Title: Selection
+Order: 1
+---
+
+The `SelectionPrompt` can be used when you want the user to select
+a single item from a provided list.
+
+<img src="../assets/images/selection.gif" style="width: 100%;" />
+
+# Usage
+
+```csharp
+// Ask for the user's favorite fruit
+var fruit = AnsiConsole.Prompt(
+    new SelectionPrompt<string>()
+        .Title("What's your [green]favorite fruit[/]?")
+        .PageSize(10)
+        .AddChoice("Apple")
+        .AddChoices(new[] {
+            "Apricot", "Avocado", 
+            "Banana", "Blackcurrant", "Blueberry",
+            "Cherry", "Cloudberry", "Cocunut",
+        }));
+
+// Echo the fruit back to the terminal
+AnsiConsole.WriteLine($"I agree. {fruit} is tasty!");
+```

docs/input/prompts/text.md

@@ -1,5 +1,6 @@
-Title: Prompt
-Order: 4
+Title: Text
+Order: 0
+RedirectFrom: prompt
 ---
 
 Sometimes you want to get some input from the user, and for this