Add a separate function to check if host is up

[vdjagilev]

Writing everytime that .HostState == "up" is an unnecessary repetition. It should be moved to the separate function and replaced everywhere

• Replaced in all templates
  • HTML
  • MD
• In golang code
  • CSV
  • Excel?
  • Graphviz

https://github.com/vdjagilev/nmap-formatter/pull/156/files