added fps counter

Makefile

@@ -0,0 +1,6 @@
+CC=gcc
+
+all: fps_counter
+
+fps_counter:
+	$(CC) fps_counter.c -lglfw -lGL -o fps_counter

fps_counter.c

@@ -0,0 +1,65 @@
+/*
+  GLFW3 frame rate counter example
+  Source: https://github.com/IIIypuk/glfw-examples
+
+  Compile: gcc fps_counter.c -lglfw -lGL
+*/
+#include <stdio.h>
+#include "GLFW/glfw3.h"
+
+int main()
+{
+  GLFWwindow *window;
+  if (!glfwInit())
+    return -1;
+
+  glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
+  window = glfwCreateWindow(400, 400, "FPS Counter", NULL, NULL);
+
+  if (!window)
+  {
+    glfwTerminate();
+    return -1;
+  }
+
+  glfwMakeContextCurrent(window);
+
+  int frames = 0;
+  double t, t0, fps;
+  char title_string[200];
+
+  t0 = glfwGetTime();
+
+  while (!glfwWindowShouldClose(window))
+  {
+    glClearColor(0.2, 0.8, 0.3, 1.0);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    glRotatef(1, 0.2, 0.2, 0);
+    glBegin(GL_POLYGON);
+      glColor3f(0.4, 0.3, 1.0);
+        glVertex3f(-0.8,  0.8, 0.0);
+        glVertex3f( 0.8,  0.8, 0.0);
+        glVertex3f( 0.8, -0.8, 0.0);
+        glVertex3f(-0.8, -0.8, 0.0);
+    glEnd();
+
+    t = glfwGetTime();
+
+    if((t - t0) > 1.0 || frames == 0)
+    {
+      fps = (double)frames / (t - t0);
+      sprintf(title_string, "FPS: %.1f FPS", fps);
+      glfwSetWindowTitle(window, title_string);
+      t0 = t;
+      frames = 0;
+    }
+    frames ++;
+
+    glfwSwapBuffers(window);
+    glfwPollEvents();
+  }
+
+  glfwTerminate();
+  return 0;
+}