[fix] issue262 fixing SQL-Hint deleting when clearing script from comments

[skryzh]

#Fixing SQL-Hint deleting when clearing script from comments
#262

What is done:

1. Added checking token type for Token.Comment.Multiline.Hint and Token.Comment.Single.Hint
2. Added some tests for covering basic behavior
3. Checked w/ tests from project
4. Checked on production SQL scripts
5. Checked as part of Airflow engine, because this library is used for splitting SQL statements before execute. And seems like this helped and Hints are working now.

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• ran the tests (pytest)
• all style issues addressed (flake8)
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[skryzh]

Hi, @andialbrecht!
Please consider to review this pr, for our project it is a vital to use SQL-Hints to help Vertica increase performance w/ complex scripts

[andialbrecht]

@skryzh hey, thanks for the pull request! Looks good so far, I've got just some nitpicks.

[andialbrecht]

LGTM! Thanks and sorry for the delay.... busy times, as usual :-D

[skryzh]

It's ok, same :D