AP_Menu: 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_Menu/AP_Menu.cpp

@@ -4,9 +4,9 @@
 // Simple commandline menu system.
 //
 
-#include <AP_Common.h>
-#include <AP_Progmem.h>
-#include <AP_HAL.h>
+#include <AP_Common/AP_Common.h>
+#include <AP_Progmem/AP_Progmem.h>
+#include <AP_HAL/AP_HAL.h>
 
 #include <stdlib.h>
 #include <ctype.h>

libraries/AP_Menu/AP_Menu.h

@@ -17,7 +17,7 @@
 #define __AP_MENU_H__
 
 #include <inttypes.h>
-#include <AP_HAL.h>
+#include <AP_HAL/AP_HAL.h>
 
 #define MENU_COMMANDLINE_MAX    32      ///< maximum input line length
 #define MENU_ARGS_MAX           3       ///< maximum number of arguments