Version 2.1 / 2.2 - Enhancements

[nasbench]

The following are changes proposed to be added in V2.1 and V2.2 of the specification

• Add Mitre d3fend namespace to tags - See update tags appendix - Add D3FEND tag namespace #147 (added in v2.1.0)
• Update SigmaHQ folder structure and reflect it in the taxonomy appendix
• Provide JSON schema for the taxonomy
• Add example field idea (discuss internally)