Change `julia-repl-cd` to project directory

[gdkrmr]

I think that julia-repl-cd should point the project directory. The same counts for the evaluation functions, e.g. julia-repl-send-line when they open a new repl buffer. Maybe there could be a configuration variable, julia-repl-default-dir that could be 'buffer or 'project by default.

VSCode uses the project directory as the working directory for the Julia process.

There was a previous discussion (#29).