AP_InertialNav: standardize inclusion of libaries headers

This commit changes the way libraries headers are included in source files:

 - If the header is in the same directory the source belongs to, so the
 notation '#include ""' is used with the path relative to the directory
 containing the source.

 - If the header is outside the directory containing the source, then we use
 the notation '#include <>' with the path relative to libraries folder.

Some of the advantages of such approach:

 - Only one search path for libraries headers.

 - OSs like Windows may have a better lookup time.

libraries/AP_InertialNav/AP_InertialNav.h

@@ -3,10 +3,10 @@
 #ifndef __AP_INERTIALNAV_H__
 #define __AP_INERTIALNAV_H__
 
-#include <AP_AHRS.h>
-#include <AP_InertialSensor.h>          // ArduPilot Mega IMU Library
-#include <AP_Baro.h>                    // ArduPilot Mega Barometer Library
-#include <AP_Buffer.h>                  // FIFO buffer library
+#include <AP_AHRS/AP_AHRS.h>
+#include <AP_InertialSensor/AP_InertialSensor.h>          // ArduPilot Mega IMU Library
+#include <AP_Baro/AP_Baro.h>                    // ArduPilot Mega Barometer Library
+#include <AP_Buffer/AP_Buffer.h>                  // FIFO buffer library
 #include "../AP_NavEKF/AP_Nav_Common.h" // definitions shared by inertial and ekf nav filters
 
 /*

libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp

@@ -1,6 +1,6 @@
 /// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
 
-#include <AP_HAL.h>
+#include <AP_HAL/AP_HAL.h>
 #include "AP_InertialNav.h"
 
 #if AP_AHRS_NAVEKF_AVAILABLE

libraries/AP_InertialNav/AP_InertialNav_NavEKF.h

@@ -10,7 +10,7 @@
 #ifndef __AP_INERTIALNAV_NAVEKF_H__
 #define __AP_INERTIALNAV_NAVEKF_H__
 
-#include <AP_Nav_Common.h>              // definitions shared by inertial and ekf nav filters
+#include <AP_NavEKF/AP_Nav_Common.h>              // definitions shared by inertial and ekf nav filters
 
 class AP_InertialNav_NavEKF : public AP_InertialNav
 {