Created string.h header; moved code to string.c

include/string.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stddef.h>
+
+void *memcpy(void *destination, const void *source, size_t num);
+
+void *memmove(void *destination, const void *source, size_t num);
+
+int memcmp(const void *ptr1, const void *ptr2, size_t num);
+
+void *memset(void *ptr, int value, size_t num);
+
+int strlen(const char *str);
+
+char *strcpy(char *destination, const char *source);