Update JSON schema generation

[goneall]

Updates the JSON Schema generator to be consistent with the current JSON example file.

• Remove the top level Document property
• Add documentNamespace

Signed-off-by: Gary O'Neall gary@sourceauditor.com

[goneall]

Generates the schema in spdx/spdx-spec#528 resolving the following issues:

• Conversion of tag-value to JSON creates a field not in the schema spdx-spec#527
• JSON schema is missing SPDXID property at the Document level spdx-spec#529
• JSON schema is missing licenseConcluded and licenseDeclared properties in the package level spdx-spec#530
• JSON schema is missing the spdxElementId element from relationships spdx-spec#531
• JSON schema/example has describesPackages/documentDescribes property that has no equivalent in the spec spdx-spec#533