VOEvent 2.1 in WD

[Baptiste Cecconi]

Dear colleagues,

A new VOEvent v2.1 document is available as a WD. 
- IVOA doc page: https://www.ivoa.net/documents/VOEvent/20230507/
- IVOA Github: https://github.com/ivoa-std/VOEvent

For this version, changes have been implemented to allow for Solar System even management. 
The proposed changes should not break the validation of VOEvent 2.0 XML content with version 2.1 schema.

The changes in the schema are documented in the schema file and in the appendix of the WD document.

Please prefer the Github repository issues for discussions, since we are bridging between several mailing lists / WG / IG. 

Cheers
Baptiste