Added ahal

This is a formatted copy of WPILib's default user-visible C++ API, with
a bit of completely unnecessary functionality stripped out. Most of the
stripping so far is only related to weird threading decisions.

Change-Id: Icbfd949b48cd115561862cb909bcc572aba0e753
diff --git a/frc971/wpilib/ahal/CounterBase.h b/frc971/wpilib/ahal/CounterBase.h
new file mode 100644
index 0000000..868dbe6
--- /dev/null
+++ b/frc971/wpilib/ahal/CounterBase.h
@@ -0,0 +1,35 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2008-2017. 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 <stdint.h>
+
+namespace frc {
+
+/**
+ * Interface for counting the number of ticks on a digital input channel.
+ * Encoders, Gear tooth sensors, and counters should all subclass this so it can
+ * be used to build more advanced classes for control and driving.
+ *
+ * All counters will immediately start counting - Reset() them if you need them
+ * to be zeroed before use.
+ */
+class CounterBase {
+ public:
+  enum EncodingType { k1X, k2X, k4X };
+
+  virtual ~CounterBase() = default;
+  virtual int Get() const = 0;
+  virtual void Reset() = 0;
+  virtual double GetPeriod() const = 0;
+  virtual void SetMaxPeriod(double maxPeriod) = 0;
+  virtual bool GetStopped() const = 0;
+  virtual bool GetDirection() const = 0;
+};
+
+}  // namespace frc