Support command alias

[vincentdephily]

It'd be nice to enable setting aliases in emlop.toml, as a shortcut for common args.

Might need a bit of trickery to avoid parsing args twice, but it shouldn't be too hard: peek the first arg, and if it matches a config entry, prepend the corresponding args before calling clap.

alias = { ll = "log --show=a --from=command", pr = "predict --show=r" }