rclnodejs v0.18.1

Bug Fix

• Run rclnodejs with Node.js (>= 10 and <=12) on appveyor #773
• Improve UX of msg generation process #759
  Developers can run npm run generate-messages manually to generate all the JavaScript messages.
• Use null-terminated string in the tests when sending a raw topic #771

Others

• Complete the contributors list #770
• Reduce README length by dividing into smaller documents #769