Would just be useful as a library?

I've hesitated to make `just` available as a library crate, since that would introduce some additional stability guarantees that I don't necessarily want to commit to.

However, it seems entirely possible that it might be useful, so I wanted to open this issue up for discussion. If you can think of ways you might use the parser, lexer, or command runner, please comment on this issue and describe your use case!

Since the `just` crate's version is used to describe the semantic version of the *binary*, I think it would probably be ideal to use a different crate for the library crate, so that it can have an independent version which doesn't move in lockstep with the binary. I am very much not excited about the idea of moving things around to facilitate this though 😂