Feature request: different verbosity levels

[dzhu]

I'd like a CLI option to suppress log messages below a given severity (as currently defined by src/Util/Logger.elm). This seems like a generally sensible thing to have once there are log levels anyway, but, for context, my particular motivation at the moment is that I'm testing out using elm-analyse as part of a pre-commit hook, along with some other checks, and the many "INFO" lines (we have a few dozen Elm files and about as many dependencies) swamp everything else. I'm certainly aware of grep, but some things in the scripting I have become more awkward when something is not a single command.

There are also a few messages generated from the TS side that could perhaps be treated similarly.

I took a quick look around the code and would maybe be able to put together a PR myself, but I figured I should open this issue first in any case to at least check that it makes sense.