Improve filtering documentation

[LaQuay]

Expand and check the SQLAlchemy Expressions in Filtering section

[dkellner]

Perfect, thank you! Can you fix the failing tests?

docs/tutorial.rst:288:77: W291 trailing whitespace
docs/tutorial.rst:289:73: W291 trailing whitespace
docs/tutorial.rst:305:1: W293 blank line contains whitespace
docs/tutorial.rst:333:1: W293 blank line contains whitespace
docs/tutorial.rst:341:1: W293 blank line contains whitespace

[LaQuay]

@dkellner Done, thanks :+1:

[dkellner]

Merged after squashing some commits to make the history cleaner.