Command-line parsing library

[marcelocantos]

Implement a library that implements command-line parsing for arr.ai programs, with support for the usual patterns, such as -f, --flag, --option=foo, --help and --version.

Wild idea

Consider opportunities to use arr.ai's grammar system to define the command-line. It might be possible to make the config look like the output of --help, e.g.:

let args = //cmdline{
    arrai - the ultimate data engine

    USAGE: arrai [global options] command [command options] [arguments...]

    COMMANDS:
       shell, i      start the arrai interactive shell
       run, r        evaluate an arrai file
       eval, e       evaluate an arrai expression
       json, jx      Convert json to arrai
       observe, o    observe an expression on a server
       serve, s      start arrai as a gRPC server
       sync, s       sync local files to a server
       transform, x  transform a stream of input data with an expression
       update, u     update a server with an expression
       help, h       Shows a list of commands or help for one command

    GLOBAL OPTIONS:
       --help, -h  show help
}.parse(//os.args);
args.command cond (
    "shell": //{./cmd_shellargs),
    "run": //{./cmd_run}(args),
    ...
)