Simpler progressbar and handle --koan=<KOAN> better

lib/meditate.ex

@@ -2,14 +2,31 @@ defmodule Mix.Tasks.Meditate do
   use Mix.Task
   alias Options
 
+  @modules [
+    Equalities,
+    Strings,
+    Tuples,
+    Lists,
+    Maps,
+    Structs,
+    PatternMatching,
+    Functions,
+    Enums,
+    Processes,
+    Tasks,
+    Agents,
+  ]
+
   def run(args) do
     Application.ensure_all_started(:elixir_koans)
     Code.compiler_options(ignore_module_conflict: true)
     Watcher.start
 
-    Tracker.start(Runner.modules)
     Options.start(args)
-    Runner.run
+
+    modules = Runner.modules_to_run
+    Tracker.start(modules)
+    Runner.run(modules)
 
     :timer.sleep(:infinity)
   end