feature: add support to split sql strings

[frste]

Fullfills issue #252: sql statements can be split by using new split_sql_string function

[frste]

Finding by my side after commit. If general approach is ok, we may shift split to _parse_sql_internally function

[amochin]

Hi @frste many thanks for your contribution!
The PR is almost ready to be merged - so feel free to publish it when you're ready (it's currently a "draft").

I'd need some minor changes and add a couple of tests though.

If possible, could you please allow me to make changes in your PR? There should be a checkbox like "allow edits from maintainers" or something like that.
Alternatively, I can merge it and continue editing on my side, but in this case your authorship of commits would get lost when I finally squash the PR. I would put your name in the commit message anyway though, so GitHub should show you as a contributor.

Please let me know which options works the best for you.