Make it easier to use inside npm script

Right now I need to do this:

  "scripts": {
        "ls": "node -e \"console.log(require('cash')('ls -l')); process.exit();\""
  }

[nfischer]

Perhaps we could implement the -c option. From Bash’s man page:

       -c        If the -c option is present, then commands are read from the first non-option argument command_string.  If  there  are
                 arguments after the command_string, they are assigned to the positional parameters, starting with $0.

[danielbayley]

@rofrol Once cash can accept -c 'input' (#75), then you can simply put script-shell = cash inside .npmrc and it should just work.