Added linear digital filters

Linear digital filter class based on code from FRC team 341

Change-Id: I4c5198e36a089e08a6d054bf1bf80392def27e23

wpilibc/shared/include/CircularBuffer.h

@@ -0,0 +1,44 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2015. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <vector>
+#include <cstddef>
+
+/**
+ * This is a simple circular buffer so we don't need to "bucket brigade" copy
+ * old values.
+ */
+template <class T>
+class CircularBuffer {
+ public:
+  CircularBuffer(size_t size);
+
+  void PushFront(T value);
+  void PushBack(T value);
+  T PopFront();
+  T PopBack();
+  void Reset();
+
+  T& operator[](size_t index);
+  const T& operator[](size_t index) const;
+
+ private:
+  std::vector<T> m_data;
+
+  // Index of element at front of buffer
+  size_t m_front = 0;
+
+  // Number of elements used in buffer
+  size_t m_length = 0;
+
+  size_t ModuloInc(size_t index);
+  size_t ModuloDec(size_t index);
+};
+
+#include "CircularBuffer.inc"