kernel: separate headers into kernel and user headers

all kernel headers have been moved from include/mango to include/kernel
and include definitions that are only relevant to kernel-space.

any definitions that are relevant to both kernel- and user-space
(i.e. type definitions, syscall IDs) have been moved to
include/mango within libmango.

vm/vm-region.c

@@ -1,11 +1,12 @@
-#include <mango/libc/stdio.h>
-#include <mango/object.h>
-#include <mango/panic.h>
-#include <mango/printk.h>
+#include <kernel/iovec.h>
+#include <kernel/libc/stdio.h>
+#include <kernel/object.h>
+#include <kernel/panic.h>
+#include <kernel/printk.h>
+#include <kernel/util.h>
+#include <kernel/vm-object.h>
+#include <kernel/vm-region.h>
 #include <mango/status.h>
-#include <mango/util.h>
-#include <mango/vm-object.h>
-#include <mango/vm-region.h>
 
 /*** STATIC DATA + MACROS *****************************************************/