--no-router flag for use in non-Phoenix projects

[halostatue]

I see the cannot found the router warning in my umbrella applications which do not have Phoenix routers, and I would also like to use Sobelow in some libraries that I maintain without seeing this warning.

If a --no-router flag is specified (or is present in configuration), then the no_router message should not be printed.

[houllette]

Great idea! Thanks for flagging this @halostatue! I will try to work on this when I can, but PRs are welcome 🙂

For help getting started, there's a bit of prior art found in #118 for adding a new CLI argument (just make sure to also take into consideration the needed hotfix for that feature in #124 😅)