Initial commit for adoc version of STIX v2.1.1

[ejratl]

As discussed in the STIX WG meeting of 24 March 2023, this pull request contains an experimental version of the STIX v2.1.1 draft in asciidoc format. This will enable us to trial spec editing using a Github work flow model. Please let me know of any errors that are spotted. Moving forward, we can refactor the document so that sections, such as the participants section are pulled in via includes. Extension and example code can also be incorporated via includes.

[ejratl]

Fixes #270 , #274, #275, #277, #278, #281, #289, #290, #291, #292, #294, #297, #299, #301, #307, #309, #312, #314, #315

[adulau]

I think we should merge it. It will be easier for contributors if there is a starting adoc document.

[ejratl]

@adulau Thanks for confirming. I will merge this now.

[SYNchroACK]

Fixes #270 , #274, #275, #277, #278, #281, #289, #290, #291, #292, #294, #297, #299, #301, #307, #309, #312, #314, #315

@ejratl @adulau some of the issues listed above were not closed automatically by this merge. Should they be closed manually?