Added multiboot header, ports methods and added new part of libc(string)

kernel/libc/string.h

@@ -0,0 +1,24 @@
+/**************************************
+ *          iceOS Kernel              *
+ * Developed by Marco 'icebit' Cetica * 
+ *            (c) 2019                *
+ *       Released under GPLv3         *
+ * https://github.com/ice-bit/iceOS   *
+ ***************************************/
+
+#ifndef _STRING_H_
+#define _STRING_H_
+
+#include <stdint.h> // For uinx_t
+#include <stddef.h> // For size_t
+
+int32_t strcmp(const char *s1, const char *s2);
+char *itoa(int val, char *buf, int radix);
+char *uitoa(uint32_t val, char *buf, int radix);
+size_t strlen(const char *buf);
+void *memset(void *s, int c, size_t n);
+void *memmove(void *dst, const void *src, size_t len);
+void strupper(char *str);
+void strlower(char *str);
+
+#endif