Option to specify languages as hx -g [build|fetch] [lang?]

[ficd0]

I find myself messing with the runtime, particularly the queries, a lot. I've also run up against this issue while adding support for new languages, or actively testing a parser I'm currently writing. Basically, it would be really nice to have an option to only fetch and build a specific grammar, like hx -g fetch markdown or hx -g build python.