Plane: added DF logging of 2nd battery voltage
Replay: fixed build with AP_NavEKF API change
Copter: minor update to AC3.2-rc14 ReleaseNotes
Camera: Added feedback message support

Now the autopilot can publish the state of the camera via the mavlink_msg_camera_feedback message.
GCS_MAVLink: add CAMERA_FEEDBACK to enum
Copter: send a camera_feedback message when there is a camera trigger
Camera: record number of pictures taken since boot

The field is useful for detecting in a GCS if a mavlink_msg_camera_feedback message was dropped.
Copter: fix camera feedback msg handling

If the camera was disabled, camera message handling would fall though to
status-text msg handling.
Camera: initialise image_index
Camera: add f to float constants
AC_WPNav: Use target yaw instead of current yaw for close waypoints
Copter: supply wp_nav with attitude_control
Copter: rework control switch debouncing
Copter: add comments to control switch debouncing
Copter: re-order init_sonar

No functional change.
ArduPilot: update README.md
ArduPilot: fixup README format
AP_AHRS: Add get_accel_ef_blended, correctly return accel_ef based on EKF attitude
AC_PosControl: use blended accel for altitude controller
AP_NavEKF: Add getAccelNED function