The lib/package/ast-open.* are almost entirely obsolete after
most of the AST utilities were removed to concentrate on ksh93
development. The only part that is both relevant and not repeated
elsewhere is AT&T's introductory blurb on ksh93.
README.md:
- Add the official AT&T ksh93 description from ast-open.html,
reformatted to Markdown with a couple of added hyperlinks.
lib/package/ast-open.README,
lib/package/ast-open.html:
- Removed. (Note that the historic ksh93 changelog in these files
is also included in src/cmd/ksh93/RELEASE).