Backward Each Word
In a given string you should reverse every word, but the words should stay in their places.
Input: A string (str).
Output: A string (str).
Examples:
assert backward_string_by_word("") == ""
assert backward_string_by_word("world") == "dlrow"
assert backward_string_by_word("hello world") == "olleh dlrow"
assert backward_string_by_word("hello world") == "olleh dlrow"
Precondition: The line consists only from alphabetical symbols and spaces.