Fix "\" problem in tutorials by using natural-language quotes.

Fix "\" problem in tutorials by using natural-language quotes.

* tutorials/TUTORIAL, tutorials/TUTORIAL.cs, tutorials/TUTORIAL.eo:
* tutorials/TUTORIAL.es, tutorials/TUTORIAL.it, tutorials/TUTORIAL.ja:
* tutorials/TUTORIAL.ko, tutorials/TUTORIAL.nl, tutorials/TUTORIAL.pl:
* tutorials/TUTORIAL.pt_BR, tutorials/TUTORIAL.ro:
* tutorials/TUTORIAL.ru, tutorials/TUTORIAL.sk, tutorials/TUTORIAL.sv:
* tutorials/TUTORIAL.th:
Avoid using ` for natural-language quotes.  Instead, work around
the problem with "\" by using non-" quotation marks appropriate
for the natural language in question, e.g., «...» for Spanish.
For English “...” could be used, but use '...' instead so that
TUTORIAL continues to be encoded in ASCII.