ustring.
    Simple C string to do my own stuff, and if u like it for yours too.
    It implents some C++ string functions such as:
    * void  push_back (Adds one character).
    * void  append    (Adds one string).
    * void  clear     (Set the content as defualt).
    * void  erase     (Removes [n, m] characters from the string).
    * void  pop_back  (Removes the last character of the string).
    * bool  bewith    (Begins/ends with...).
    * bool  contains  (Check if the string has some string into it).
    * char* substring (Gets the [n, m] part of the string).
    * void  overwrite (Overwrites n characters of the string for the new content).
    * char  at        (Returns the character at the pos given, null character if pos' outta range).
    * void  kill      (Dealloc the content of the struct).

    All functions that requires indexes include them into the range, so if the function looks like
    void name (size_t n, size_t m) it'll be [n, m].