Fix: unsolicited spreading/flattening of arguments

[Kareem-Medhat]

Program currently spreading/expanding quoted, multi-word arguments instead of forwarding them to script.

Changes

• AppArgs now stores arguments in a Vec<String> rather than a String
• Introduces new crate, shlex, to correctly parse arguments passed in interactive
  mode into a Vec<String>
• Changes run_command function to correctly forward the arguments
• If user passes invalid arguments in interactive mode ( such as leaving an open quote ) the user is warned and prompted again until the user passes valid arguments or exits

Behavior before changes

dum run foo "first arg" "second"
$ foo
$ node stuff/example-script first arg second
from example [ 'first', 'arg', 'second' ] # ❌ 3 arguments

Behavior after changes (desired behavior)

dum run foo "first arg" "second"
$ foo
$ node stuff/example-script "first arg" second
from example [ 'first arg', 'second' ] # ✅ 2 arguments

Fixes

fixes #59