Add a new test case about escaping double quotes in a triple quoted string.

This replaces a simple method in the test suite with a new test to test escaping quotes in a triple quoted string. I think this is a good case to learn more about when to escape double quotes in a triple quoted string.

The old function
```
def but_quotes_at_the_end_of_a_triple_quoted_string_are_still_tricky(self):
        string = """Hello "world\""""
```
This pull request is based on issue #61
Please close the issue once you accept the pull request. 

Thanks
Shishir Kakaraddi