Sapling: Add functionality for web and demo

- Web: Add `serve` functionality, which starts a simple Rack application
to serve a template page. Template still needs work.

- Demo: add `example` option, which starts the CLI using the "Example
Quest!" tree

lib/sapling.rb

@@ -1,5 +1,7 @@
 #!/usr/bin/env ruby
+# frozen string literal: true
 
+require 'rack'
 require 'thor'
 require 'yaml'
 
@@ -7,6 +9,7 @@ Dir[File.join(__dir__, 'sapling', '*.rb')].each { |file| require file }
 
 # The main Sapling interface.
 class Sapling < Thor
+  # CLI-based options
   desc 'read TREE', 'Load and traverse the TREE'
   def read(file)
     puts 'Welcome to Sapling, a Dialogue Tree Utility.'
@@ -30,10 +33,16 @@ class Sapling < Thor
     gardner.plant
   end
 
+  # Web-based options
   desc 'serve TREE', 'Load TREE in a web-based interface'
-  def serve(tree)
-    exit unless verify_tree(tree)
-    puts 'Sinatra will be cool.'
+  def serve(file)
+    exit unless verify_tree(file)
+    tree = Gardner::Plot.new(YAML.load_file(file))
+    Rack::Server.new(
+      app: Greenhouse.new(tree),
+      server: 'webrick',
+      Port: 9000
+    ).start
   end
 
   desc 'export TREE', 'Save a portable HTML version of TREE'
@@ -41,4 +50,15 @@ class Sapling < Thor
     exit unless verify_tree(tree)
     puts 'Cool feature, bro!'
   end
+
+  # Miscellaneous options
+  desc 'example', 'Play Example Quest!'
+  def example
+    file = File.join(__dir__, '..', 'var', 'trees', 'example_quest.yaml')
+    puts 'Welcome to Sapling, a Dialogue Tree Utility.'
+    exit unless verify_tree(file)
+    tree = Gardner::Plot.new(YAML.load_file(file))
+    speaker = Dialogue::Speaker.new(tree, false)
+    speaker.conversation
+  end
 end