Rename Gyro to AnalogGyro and make Gyro an interface.

Refactor common implementation parts of AnalogGyro into GyroBase.

This will make it possible to add digital gyros in a similar way to how
digital accelerometers were added.

Change-Id: I437ef259e9ecb81f18a91a95c5a58b6607db5e15

wpilibj/wpilibJava/src/main/java/edu/wpi/first/wpilibj/interfaces/Gyro.java

@@ -0,0 +1,56 @@
+/*----------------------------------------------------------------------------*/
+/* 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. */
+/*----------------------------------------------------------------------------*/
+package edu.wpi.first.wpilibj.interfaces;
+
+/**
+ * Interface for yaw rate gyros
+ */
+public interface Gyro {
+  /**
+   * Initialize the gyro. Calibrate the gyro by running for a number of samples
+   * and computing the center value. Then use the center value as the
+   * Accumulator center value for subsequent measurements. It's important to
+   * make sure that the robot is not moving while the centering calculations are
+   * in progress, this is typically done when the robot is first turned on while
+   * it's sitting at rest before the competition starts.
+   */
+  public void initGyro();
+
+  /**
+   * Reset the gyro. Resets the gyro to a heading of zero. This can be used if
+   * there is significant drift in the gyro and it needs to be recalibrated
+   * after it has been running.
+   */
+  public void reset();
+
+  /**
+   * Return the actual angle in degrees that the robot is currently facing.
+   *
+   * The angle is based on the current accumulator value corrected by the
+   * oversampling rate, the gyro type and the A/D calibration values. The angle
+   * is continuous, that is it will continue from 360 to 361 degrees. This
+   * allows algorithms that wouldn't want to see a discontinuity in the gyro
+   * output as it sweeps past from 360 to 0 on the second time around.
+   *
+   * @return the current heading of the robot in degrees. This heading is based
+   *         on integration of the returned rate from the gyro.
+   */
+  public double getAngle();
+
+  /**
+   * Return the rate of rotation of the gyro
+   *
+   * The rate is based on the most recent reading of the gyro analog value
+   *
+   * @return the current rate in degrees per second
+   */
+  public double getRate();
+
+  /**
+   * Free the resources used by the gyro
+   */
+  public void free();
+}