Added an Accelerometer interface

ADXL345_I2C, ADXL345_SPI, and BuiltInAccelerometer implement this interface.

The analog accelerometer class Accelerometer was renamed to
AnalogAccelerometer.

Change-Id: Iaae79d582a24c36c372f5fd4ea6df37be289b9c1

wpilibc/wpilibC++/include/interfaces/Accelerometer.h

@@ -0,0 +1,52 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2014. 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 $(WIND_BASE)/WPILib.  */
+/*----------------------------------------------------------------------------*/
+#pragma once
+
+/**
+ * Interface for 3-axis accelerometers
+ */
+class Accelerometer
+{
+public:
+	virtual ~Accelerometer() {};
+
+	enum Range
+	{
+		kRange_2G = 0,
+		kRange_4G = 1,
+		kRange_8G = 2,
+		kRange_16G = 3
+	};
+
+	/**
+	 * Common interface for setting the measuring range of an accelerometer.
+	 *
+	 * @param range The maximum acceleration, positive or negative, that the
+	 * accelerometer will measure.  Not all accelerometers support all ranges.
+	 */
+	virtual void SetRange(Range range) = 0;
+
+	/**
+	 * Common interface for getting the x axis acceleration
+	 *
+	 * @return The acceleration along the x axis in g-forces
+	 */
+	virtual double GetX() = 0;
+
+	/**
+	 * Common interface for getting the y axis acceleration
+	 *
+	 * @return The acceleration along the y axis in g-forces
+	 */
+	virtual double GetY() = 0;
+
+	/**
+	 * Common interface for getting the z axis acceleration
+	 *
+	 * @return The acceleration along the z axis in g-forces
+	 */
+	virtual double GetZ() = 0;
+};