Add checker for TODO comments without detail/assignee

[liamg]

Resolves #434

[cristaloleg]

sgtm

[quasilyte]

I think it should be marked with an "opinionated" tag, just in case.
It's not always sensible to require this rule to be followed.
We can merge PR and add this tag separately though, as it's marked with experimental anyway.

[liamg]

@quasilyte Thanks, I've addressed your comment. Sorry for the delay. It looks like the cg.List[...].Text fields include the comment initialisers (// and /*) so I've adjusted the regex to take this into account and everything seems to work.

[quasilyte]

I have a few more suggestions, but I'm OK with merging it as is, so they can be addressed later.
One of my questions is: this is probably more style-related than correctness-related. So the "diagnostic" tag is quite misleading.

[liamg]

Cool, I changed it to style and added opinionated too.