TODO linter

[lnihlen]

Write a program that scans all input source code (including Bison, Ragel, C++, sclang) for TODO comments, and generates an error for any TODOs that don't have an associated bug link. So

// TODO(https://github.com/hadron-sclang/hadron/issues/110): short explanation of issue

is the only acceptable format of TODO comment according to the script. We can put this in as part of the linting stage.

[lnihlen]

For bonus points you could also check if the issue is still open/valid, and error out if its been closed..

[lnihlen]

Probably best to re-use something like: https://github.com/todogroup/repolinter

[lnihlen]

or this one: https://github.com/preslavmihaylov/todocheck