Little improvements & some bugfixes #36

Bugfixes

• #5: Fix CSV formatter skipping down hosts

Features

• #7: Rename down-hosts output option
• #12: Increase unit test coverage
• #11: Implement json-pretty print option
• #8: Add new skip output options

Other

• #2: Move types formatter package
• #10: Remove unused variable from root.go validate function
• #6: Add build status badge
• #3: Add table of contents to the README
• #28: Cleanup
• #9: Add matrix strategy for ci workflow
• #20: Add codeclimate badge
• #4: Add nmap-formatter examples with jq tool