Part of #62: automatically detect schema from $schema property in JSON data, switch order of CLI arguments
Part of #62: support relative schema paths
Part of #62: support http/https schemas
Fix #62: detect JSON schema from HTTP headers of data file
Disallow persistent HTTP connections
Resolve relative schema path to cwd(), not json file
Merge pull request #75 from netresearch/ASTV-22

Fix for #62, #63, #64: automatically detect schema URL