feat: extract todos

[upstartjohnvandivier]

should a code audit tool have the ability to extract TODO comments from the code?

i sure think so!

let me know if y'all are open to a PR. I'm imagining single-line support only atm. If the config file specifies tool.pylama.todo-file then we will by default collect text after TODO: and dup those lines log-style plaintext into the destination file.

could later be generalized to comment extraction of non-todo comments but meh for now nah