added a circle button for the loop stations and the beat player

circle_button.py

@@ -0,0 +1,21 @@
+import pygame
+from colors import *
+import math
+
+class CircleButton:
+
+    def __init__(self, gui, x, y, radius):
+        self.screen = gui.screen
+        self.x = x
+        self.y = y
+        self.radius = radius
+        self.color = color_primary
+
+    def check_click(self, pos, action):
+        if math.sqrt(math.pow(pos[0] - self.x, 2) +
+                     math.pow(pos[1] - self.y, 2)) < self.radius:
+            action()
+
+    def display(self):
+        pygame.draw.circle(self.screen, self.color,
+                                   (self.x, self.y), self.radius)