Added progress bar samples

samples/progress_bar_set_progress.cpp

@@ -0,0 +1,38 @@
+#include <indicators/progress_bar.hpp>
+#include <thread>
+#include <chrono>
+
+int main() {
+  indicators::ProgressBar bar;
+  
+  // Configure the 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_postfix_text("Getting started");
+  bar.set_foreground_color(indicators::Color::GREEN); 
+  
+  // Update bar state
+  
+  bar.set_progress(10); // 10% done
+  
+  // do some work
+  std::this_thread::sleep_for(std::chrono::milliseconds(100));
+  
+  bar.set_progress(30); // 30% done
+  
+  // do some more work             
+  std::this_thread::sleep_for(std::chrono::milliseconds(600));
+  
+  bar.set_progress(65); // 65% done
+  
+  // do final bit of work
+  std::this_thread::sleep_for(std::chrono::milliseconds(300));
+  
+  bar.set_progress(100); // all done
+  
+  return 0;
+}