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.

test/obj.c

@@ -1,7 +1,7 @@
-#include <mango/object.h>
-#include <mango/printk.h>
-#include <mango/init.h>
-#include <mango/libc/stdio.h>
+#include <kernel/object.h>
+#include <kernel/printk.h>
+#include <kernel/init.h>
+#include <kernel/libc/stdio.h>
 
 #define TEST_CAST(p) OBJECT_C_CAST(struct test_object, base, &test_type, p)
 

test/test.c

@@ -1,5 +1,5 @@
-#include <mango/init.h>
-#include <mango/printk.h>
+#include <kernel/init.h>
+#include <kernel/printk.h>
 
 int run_all_tests(void)
 {