Added progress bar samples

samples/multi_threaded_bar.cpp

@@ -0,0 +1,63 @@
+#include <indicators/progress_bar.hpp>
+#include <vector>
+
+int main() {
+
+  indicators::ProgressBar bar;
+  bar.set_bar_width(50);
+  bar.start_bar_with("[");
+  bar.fill_bar_progress_with("■");
+  bar.lead_bar_progress_with("■");
+  bar.fill_bar_remainder_with("-");
+  bar.end_bar_with("]");
+  bar.set_foreground_color(indicators::Color::YELLOW);
+
+  // As configured, the bar will look like this:
+  //
+  // [■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■-------------] 70%
+  //
+  //
+  
+  std::atomic<size_t> index{0};
+  std::vector<std::string> status_text =
+    {
+     "Rocket.exe is not responding",
+     "Finding a replacement engineer",
+     "Buying more snacks",
+     "Assimilating the modding community",
+     "Crossing fingers",
+     "Porting KSP to a Nokia 3310"
+  };
+  
+  // Let's say you want to append some status text to the right of the progress bar
+  // You can use bar.set_postfix_text(...) to append text to the right
+  //
+  // [■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■-------------] 70% Finding a replacement engineer
+  //                                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  //
+  //  
+
+  auto job = [&bar, &index, &status_text]() {
+    while (true) {
+      if (bar.is_completed()) {
+        break;
+      }
+      bar.set_postfix_text(status_text[index % status_text.size()]);
+      bar.tick();
+      index += 1;
+      std::this_thread::sleep_for(std::chrono::milliseconds(200));
+    }
+  };
+
+  std::thread first_job(job);
+  std::thread second_job(job);
+  std::thread third_job(job);
+  std::thread last_job(job);
+
+  first_job.join();
+  second_job.join();
+  third_job.join();
+  last_job.join();
+  
+  return 0;
+}