Make modern AsciiDoc the target for `asciidoc`.

The AsciiDoc community now regards the dialect parsed by `asciidoctor`
as the official AsciiDoc syntax, so it should be the target of our
`asciidoc` format.

Closes #8936.

The `asciidoc` output format now behaves like `asciidoctor` used to.
`asciidoctor` is a deprecated synonynm. For the old `asciidoc` behavior
(targeting the Python script), use `asciidoc_legacy`.

The templates have been consolidated. Instead of separate
`default.asciidoctor` and `default.asciidoc` templates, there is
just `default.asciidoc`.

Text.Pandoc.Writers.AsciiDoc API changes:

- `writeAsciiDoc` now behaves like `writeAsciiDoctor` used to.
- `writeAsciiDoctor` is now a deprecated synonym for `writeAsciiDoc`.
- New exported function `writeAsciiDocLegacy` behaves like
  `writeAsciDoc` used to.

2 files changed, 3 insertions, 43 deletions

diff --git a/data/templates/default.asciidoc b/data/templates/default.asciidoc
index ebe70914d..e20384989 100644
--- a/data/templates/default.asciidoc
+++ b/data/templates/default.asciidoc
@@ -17,6 +17,9 @@ $endif$
 $if(toc)$
 :toc:
 $endif$
+$if(math)$
+:stem: latexmath
+$endif$
 
 $endif$
 $if(abstract)$
diff --git a/data/templates/default.asciidoctor b/data/templates/default.asciidoctor
deleted file mode 100644
index e20384989..000000000
--- a/data/templates/default.asciidoctor
+++ /dev/null
@@ -1,43 +0,0 @@
-$if(titleblock)$
-= $title$
-$if(author)$
-$for(author)$$author$$sep$; $endfor$
-$if(date)$
-$date$
-$endif$
-$elseif(date)$
-:revdate: $date$
-$endif$
-$if(keywords)$
-:keywords: $for(keywords)$$keywords$$sep$, $endfor$
-$endif$
-$if(lang)$
-:lang: $lang$
-$endif$
-$if(toc)$
-:toc:
-$endif$
-$if(math)$
-:stem: latexmath
-$endif$
-
-$endif$
-$if(abstract)$
-[abstract]
-== Abstract
-$abstract$
-
-$endif$
-$for(header-includes)$
-$header-includes$
-
-$endfor$
-$for(include-before)$
-$include-before$
-
-$endfor$
-$body$
-$for(include-after)$
-
-$include-after$
-$endfor$