Return exit code in bundler.cmd

Bundler.cmd now passes the exit code from bundler.js back to the OS.
Without the exit code to indicate errors using bundler.cmd in a
post-build step fails silently.
Ignore comments when rendering bundles

The Render[JS|CSS]Bundle functions didn't properly ignore comment lines,
causing the rendering to fail when advanced options or comments are used
in the bundle.
Merge pull request #57 from AVee/master

Fixes for comment handling and post-build command.