Merge pull request #1164 from 0xc0170/fix_buffer_index

CircularBuffer - volatile full flag + indexes

Author: 0xc0170

libraries/mbed/api/CircularBuffer.h

@@ -88,9 +88,9 @@ class CircularBuffer {
 
 private:
     T _pool[BufferSize];
-    CounterType _head;
-    CounterType _tail;
-    bool _full;
+    volatile CounterType _head;
+    volatile CounterType _tail;
+    volatile bool _full;
 };
 
 }