go fmt
it is sufficient to check for "http"

"https" is covered as well
use constants for type of check result Info, Warning, Error, StructuralError
Check returns an array of messages AND a generic error
Enhancements in understood command line switches

  - of - filename of file into which JSON stream will be saved
  - version - according to which OGD-Version will the JSON data be checked?
  - follow - check http-links in the JSON-metadata?