Adds popular tool npm-run-all for running scripts.

Benefits:

• Single script to run all types of linting in parallel (run-p is alias for npm-run-all --parallel)
• Uses double quotes instead of single quotes for better cross-platform support
• Uses npm-run-all instead of && for better cross-platform support

  Cross platform. We sometimes use & to run multiple command in parallel, but cmd.exe (npm run-script uses it by default) does not support the &. Half of Node.js users are using it on Windows, so the use of & might block contributions. npm-run-all --parallel works well on Windows as well.