Substitutes the replacement string/character at the given index in the
    given string, returns the modified string.

    **Examples**:
    ::
        auxly.stringy.subat("bit", 2, "n")

def subat(orig, index, replace):
    """Substitutes the replacement string/character at the given index in the
    given string, returns the modified string.

    **Examples**:
    ::
        auxly.stringy.subat("bit", 2, "n")
    """
    return "".join([(orig[x] if x != index else replace) for x in range(len(orig))])