Move all include files to src/include

- 86Box's own headers go to /86box
- munt's public interface goes to /mt32emu
- all slirp headers go to /slirp (might want to consider using only its public inteface)
- single file headers from other projects go in include root

src/printer/prt_ps.c

@@ -22,15 +22,15 @@
 #include <stdlib.h>
 #include <string.h>
 #include <wchar.h>
-#include "86box.h"
-#include "language.h"
-#include "lpt.h"
-#include "timer.h"
-#include "pit.h"
-#include "plat.h"
-#include "plat_dynld.h"
-#include "ui.h"
-#include "prt_devs.h"
+#include <86box/86box.h>
+#include <86box/language.h>
+#include <86box/lpt.h>
+#include <86box/timer.h>
+#include <86box/pit.h>
+#include <86box/plat.h>
+#include <86box/plat_dynld.h>
+#include <86box/ui.h>
+#include <86box/prt_devs.h>
 
 #if defined(_WIN32) && !defined(__WINDOWS__)
 #define __WINDOWS__