Added progress spinner sample

samples/progress_spinner.cpp

@@ -0,0 +1,38 @@
+#include <indicators/progress_spinner.hpp>
+
+int main() {
+
+  // Hide cursor
+  std::cout << "\e[?25l";
+
+  indicators::ProgressSpinner spinner;
+  
+  // Configure the spinner
+  spinner.set_postfix_text("Checking credentials");
+  spinner.set_foreground_color(indicators::Color::YELLOW);
+  spinner.set_spinner_states({"⠈", "⠐", "⠠", "⢀", "⡀", "⠄", "⠂", "⠁"});
+  
+  // Update spinner state
+  auto job = [&spinner]() {
+    while (true) {
+      if (spinner.is_completed()) {
+        spinner.set_foreground_color(indicators::Color::GREEN);
+        spinner.set_prefix_text("✔");
+        spinner.hide_spinner();
+        spinner.hide_percentage();
+        spinner.set_postfix_text("Authenticated!");
+        spinner.mark_as_completed();
+        break;
+      } else
+        spinner.tick();
+      std::this_thread::sleep_for(std::chrono::milliseconds(40));
+    }
+  };
+  std::thread thread(job);
+  thread.join();
+
+  // Show cursor
+  std::cout << "\e[?25h";    
+
+  return 0;
+}