Port to Python3 and fix flake8 errors

[deadbits]

• Updated the example to use Python3
• Now accepts arguments at command line for base url, api key, and selector
  • validates base url to ensure its a real domain name
• Fixed flake8 spacing (e.g., baseurl,apikey,selector -> baseurl, apikey, select
• Fixed flake8 imports (single import per line)
• Fixed flake8 commenting (double space after code line, space between # and comment text
• Standardize use of single / double quote across script
• Added comment to function describing what it does
• Added JSON syntax highlighting / pretty-print for output of data
• Handle HTTP exceptions when requests calls are made
• Remove extra / unneeded creation of searchurl

[deadbits]

Thank you!