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/page.c

@@ -1,8 +1,8 @@
-#include <mango/libc/string.h>
-#include <mango/memblock.h>
-#include <mango/printk.h>
-#include <mango/types.h>
-#include <mango/vm.h>
+#include <kernel/libc/string.h>
+#include <kernel/memblock.h>
+#include <kernel/printk.h>
+#include <kernel/types.h>
+#include <kernel/vm.h>
 
 /* Pre-calculated page order -> size conversion table */
 static size_t page_order_bytes[] = {