extension-tool: Use asciidoctor for manpage

The Python implementation of Asciidoc is abandoned and stuck with Python 2.
Asciidoctor is a maintained implementation written in Ruby.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/992

subprojects/extensions-tool/man/meson.build

@@ -1,7 +1,7 @@
 custom_target('gnome-extensions.1',
-  input: ['gnome-extensions.txt', 'stylesheet.xsl'],
+  input: 'gnome-extensions.adoc',
   output: 'gnome-extensions.1',
-  command: [a2x, '-D', '@OUTDIR@', '--xsl-file', '@INPUT1@', '-f', 'manpage', '@INPUT0@'],
+  command: [asciidoctor, '-D', '@OUTDIR@', '-b', 'manpage', '@INPUT@'],
   install_dir: mandir + '/man1',
   install: true
 )

subprojects/extensions-tool/man/stylesheet.xsl

@@ -1,27 +0,0 @@
-<?xml version='1.0'?>
-<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
-		version='1.0'>
-<xsl:import href="http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"/>
-
-<xsl:template match="variablelist/title">
-  <xsl:text>.PP&#10;</xsl:text>
-  <xsl:call-template name="bold">
-    <xsl:with-param name="node" select="."/>
-    <xsl:with-param name="context" select=".."/>
-  </xsl:call-template>
-  <xsl:text>&#10;</xsl:text>
-</xsl:template>
-
-<xsl:template match="varlistentry[preceding-sibling::title]">
-  <xsl:if test="not(preceding-sibling::varlistentry)">
-    <xsl:text>.RS 4&#10;</xsl:text>
-    <!-- comment out the leading .PP added by the original template -->
-    <xsl:text>.\"</xsl:text>
-  </xsl:if>
-  <xsl:apply-imports/>
-  <xsl:if test="position() = last()">
-    <xsl:text>.RE&#10;</xsl:text>
-  </xsl:if>
-</xsl:template>
-
-</xsl:stylesheet>

subprojects/extensions-tool/meson.build

@@ -36,7 +36,7 @@ if bash_completion.found()
 endif
 
 if get_option('man')
-  a2x = find_program('a2x')
+  asciidoctor = find_program('asciidoctor')
 
   subdir('man')
 endif