Add progress reporting to CLI

Closes #143

DiscordChatExporter.Cli/Internal/InlineProgress.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace DiscordChatExporter.Cli.Internal
+{
+    internal class InlineProgress : IProgress<double>, IDisposable
+    {
+        private readonly int _posX;
+        private readonly int _posY;
+
+        public InlineProgress()
+        {
+            _posX = Console.CursorLeft;
+            _posY = Console.CursorTop;
+        }
+
+        public void Report(double progress)
+        {
+            Console.SetCursorPosition(_posX, _posY);
+            Console.WriteLine($"{progress:P1}");
+        }
+
+        public void Dispose()
+        {
+            Console.SetCursorPosition(_posX, _posY);
+            Console.WriteLine("Completed ✓");
+        }
+    }
+}