Improve docs and examples to make users more aware of SQL injections

[almarklein]

Done:

• Clearer names for parameter names and code variables.
• Explicitly document all function parameters, and mark those that are potentially unsafe.
• Update all examples that used the unsafe form (even if it was just using a constant).
• Added a section to the docs on SQL injection.

Also:

• New black.
• Update CI.