Add .bc-ignore for code pathes

[klartext79]

A lot of custom project setups contain Different targets in root folder. Frameworks, External included subprojects (git submodules) and so on.

With this config all of them are scanned.

[update.code]
codePath = "."

Instead of adding support for multiple pathes like mentioned here:
Use multiple codePath locations

I would prefer another approach. The git ignore way.

If one could either add an empty .bc-ignore file to each folder that shouldn't be scanned (recursively) OR add a .bc-ignore file at root level with pathes to be ignored.

[Jeehut]

Thank you, great idea. Upvoted at first, but then saw you upvoted yourself, so removed mine to balance your vote out. 😅 Will consider this for the next major release at least. Good catch to use the same name as the existing #bc-ignore!, it's intuitive to use that I guess. 👍

[Jeehut]

Note that I just commented on #155 that I think it's an important feature we should ship before the next major version. That doesn't mean though that we shouldn't add this feature as well as they are not mutually exclusive. They could be used both as the one is listing opt-in routes and this one is opt-out. I'm not sure if we should add files, we could also just add another option to exclude routes to keep things consistent. But that's a design choice to be made when implementing this.