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.

kernel/printk.c

@@ -1,7 +1,7 @@
-#include <mango/printk.h>
-#include <mango/locks.h>
-#include <mango/console.h>
-#include <mango/libc/stdio.h>
+#include <kernel/printk.h>
+#include <kernel/locks.h>
+#include <kernel/console.h>
+#include <kernel/libc/stdio.h>
 #include <stdarg.h>
 
 #define LOG_BUFFER_SIZE 0x40000