Add <unistd.h> with read, write and close functions

src/include/unistd.h

@@ -0,0 +1,11 @@
+#ifndef _UNISTD_H
+#define _UNISTD_H
+
+#include <stddef.h>
+#include <sys/types.h>
+
+ssize_t read(int fildes, void *buf, size_t nbyte);
+ssize_t write(int fildes, const void *buf, size_t nbyte);
+int close(int fildes);
+
+#endif

src/unistd.c

@@ -0,0 +1,14 @@
+#include <unistd.h>
+#include <liblinux.h>
+
+ssize_t read(int fildes, void *buf, size_t nbyte) {
+  return sys_read(fildes, buf, nbyte);
+}
+
+ssize_t write(int fildes, const void *buf, size_t nbyte) {
+  return sys_write(fildes, buf, nbyte);
+}
+
+int close(int fildes) {
+  return sys_close(fildes);
+}