Deprecate and define EOL/EOS path for XML

This issue is to discuss the possibility for eliminating support for XML

Currently, XML and JSON Schemas have some inconsistencies. Some of the inconsistencies are described in #146. There are many benefits to removing support for XML, including:

* Eliminate unnecessary complexity in libraries and tools supporting CycloneDX
* Reduce the number of dependencies needed in libraries/tools
* Decrease the amount of time needed by maintainers to keep libraries/tools up to date with current spec versions
* Decrease the probability of defects introduced in libraries/tools supporting CycloneDX
* Decrease the amount of time necessary for CycloneDX/Ecma standards development, review, and approval

If there is agreement by the CycloneDX Core Working Group and by Ecma TC54, we will need to define a deprecation path that leads to the eventual EOL/EOS for XML.

Community feedback necessary. Lets the comments commence...