Better handling of subprocess args and stderr redirection

[YodaDaCoda]

• Pipe output instead of console.error
  • console.error adds extra newlines and possibly does other formatting which we don't want
• By using child_process.spawn instead of child_process.exec, we don't have to do so much manual handling of args.
  • This was causing me problems trying to execute PMD as flags were getting sent wrapped in quotes.

[NLueg]

Thank you very much for your PR and especially the nice refactoring you made!