Improve progress bar

This improves progress bar by:
- Adding progress percentage
- Calculating progress bar underline based on the text length of progress bar

lib/display.ex

@@ -56,11 +56,13 @@ defmodule Display do
   end
 
   defp format(failure, module, name) do
+    progress_bar = ProgressBar.progress_bar(Tracker.summarize())
+    progress_bar_underline = String.duplicate("-", String.length(progress_bar))
     """
     #{Intro.intro(module, Tracker.visited())}
     Now meditate upon #{format_module(module)}
-    #{ProgressBar.progress_bar(Tracker.summarize())}
+    #{progress_bar}
-    ----------------------------------------
+    #{progress_bar_underline}
     #{name}
     #{Failure.format_failure(failure)}
     """

lib/display/progress_bar.ex

@@ -4,14 +4,19 @@ defmodule Display.ProgressBar do
 
   def progress_bar(%{current: current, total: total}) do
     arrow = calculate_progress(current, total) |> build_arrow
+    progress_percentage = calculate_percentage(current, total)
 
-    "|" <> String.pad_trailing(arrow, @progress_bar_length) <> "| #{current} of #{total}"
+    "|" <> String.pad_trailing(arrow, @progress_bar_length) <> "| #{current} of #{total} -> #{progress_percentage}% complete"
   end
 
   defp calculate_progress(current, total) do
     round(current / total * @progress_bar_length)
   end
 
+  defp calculate_percentage(current, total) do
+    Float.round(current / total * 100, 1)
+  end
+
   defp build_arrow(0), do: ""
 
   defp build_arrow(length) do