Expose the `configParser` function

[seagreen]

Right now if you're making an executable you can either use defaultMain to get preset command line options, or you can write your own from scratch, but there's no way to do what bin/Main.hs does and augment the configParser with additional command line options.

This could be useful for writing a benchmark for a specific problem domain where you want all the normal configParser options available, plus some others for the problem domain.

PS: I'm incredibly excited about this project.

[seagreen]

On thing this won't help with is projects that need to use something like configParser but with adjustments.

For instance I realized my current project needs to change it to note that --timeout is set by default to X seconds.

So it's most convenient for me to just copy the code from common/Parser.hs into my project and modify it. If most other projects end up doing the same then exposing configParser isn't necessary.