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/memblock.c

@@ -20,9 +20,9 @@
     software without specific prior written permission.
  */
 #include <limits.h>
-#include <mango/libc/string.h>
-#include <mango/memblock.h>
-#include <mango/types.h>
+#include <kernel/libc/string.h>
+#include <kernel/memblock.h>
+#include <kernel/types.h>
 #include <stdbool.h>
 
 #define MIN(a, b)  ((a) < (b) ? (a) : (b))