Create a run subcommand, not just run-compat

[rocketnia]

We should create a rainbow-js-args run [args...] subcommand that has functionality similar to rainbow-js-args run-compat [args...] for executing Arc programs in batch mode and starting REPLs.

By allowing ourselves to change the CLI syntax, we can probably achieve a bit more flexibility than what Java Rainbow supports, such as the way Racket's CLI supports interleaving files to load and expressions to evaluate. Java Rainbow's CLI can already execute multiple files and multiple expressions, but it executes every file before executing any of the expressions.