feat: expand user mode, add DOOM game, add manpages

programs/include/libc/errno.h

@@ -0,0 +1,29 @@
+#ifndef _LIBC_ERRNO_H
+#define _LIBC_ERRNO_H
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int errno;
+
+#define ENOENT  2
+#define EIO     5
+#define ENOMEM  12
+#define EACCES  13
+#define EINVAL  22
+#define ERANGE  34
+#define ENOSYS  38
+#define EISDIR  21
+#define ENOTDIR 20
+#define EEXIST  17
+#define EBADF   9
+#define EPERM   1
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _LIBC_ERRNO_H */