Mutable-String

Create MutableString class that

1. will inherit from MutableSequence from collections.abc

2. will have following methods: __ getitem__(self, item), __ setitem__(self, item, value), __ str__(self), __ len__(self), __ iter__(self), __ repr__(self), __ add__(self, string), __ len__(self), __ iter__(self)

   title(self), capitalize(self), center(self, width, fill=None),

   upper(self), lower(self), startswith(self, string), endswith(self, string),

   find(self, string, start=None, end=None), rfind(self, s, start=None, end=None),

   index(self, string, start=None, end=None), rindex(self, string, start=None, end=None),

   split(self, symbol), replace(self, old, new), rreplace(self, old, new),

   isdigit(self), isalpha(self), isalnum(self), islower(self), isupper(self), isspace(self), istitle(self),

   join(self, array), format(self, * args, ** kwargs),

   ord(self, c), chr(self, d),

   count(self, string, start=None, end=None),

   lstrip(self, c=None), rstrip(self, c=None), strip(self, c=None)