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, 2 insertions, 2 deletions

diff --git a/test/command/8437.md b/test/command/8437.md
index fcd416239..ab416955d 100644
--- a/test/command/8437.md
+++ b/test/command/8437.md
@@ -1,5 +1,5 @@
 ```
-% pandoc -f markdown -t asciidoctor
+% pandoc -f markdown -t asciidoc
 [![alt](https://img.shields.io/badge/License-Apache%202.0-blue.svg "title")](http://www.apache.org/licenses/LICENSE-2.0)
 ^D
 http://www.apache.org/licenses/LICENSE-2.0[image:https://img.shields.io/badge/License-Apache%202.0-blue.svg[alt,title="title"]]
diff --git a/test/command/8665.md b/test/command/8665.md
index 15d926d26..8f54efedd 100644
--- a/test/command/8665.md
+++ b/test/command/8665.md
@@ -1,5 +1,5 @@
 ```
-% pandoc -f docbook -t asciidoctor
+% pandoc -f docbook -t asciidoc
 <informaltable frame="all" rowsep="1" colsep="1">
     <tgroup cols="1">
         <thead>