Document the structure of ScanCode's JSON output

[jdaguil]

There should be documentation for the ScanCode structure in the JSON output. Sometimes it's difficult to know what the data types are for the output.

For example, when the value is null or an empty array:

"date": null,
"mime_type": null,
"scan_errors": [],
"copyrights": [
        {
          "statements": [
            "Copyright (c) 2002-2004 Dmitriy Anisimkov"
          ],
          "holders": [
            "Dmitriy Anisimkov"
          ],
          "authors": [],
          "start_line": 4,
          "end_line": 4
        }

[pombredanne]

I generated some JSON schema from schematics for ScanCode... I will commit this later though let me paste these here for now.

json-schemas.zip

[pombredanne]

https://github.com/nexB/scancode-toolkit/tree/develop/etc/scripts/sch2js now contains a script and generated JSON schema for the Package models.