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.

arch/user/init.c

@@ -1,11 +1,11 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <mango/init.h>
-#include <mango/memblock.h>
-#include <mango/vm.h>
-#include <mango/object.h>
-#include <mango/printk.h>
+#include <kernel/init.h>
+#include <kernel/memblock.h>
+#include <kernel/vm.h>
+#include <kernel/object.h>
+#include <kernel/printk.h>
 #include <arch/stdcon.h>
 #include <sys/mman.h>