set outfilesuffix to match extension of input filename

- set outfilesuffix to match extension of input filename
- update test for inter-document xref
- set docname attribute
- add test for docname attribute value
- pass attributes as a hash to ensure docname value is properly escaped

lib/github/markups.rb

@@ -28,8 +28,19 @@
 end
 
 markup(::GitHub::Markups::MARKUP_ASCIIDOC, :asciidoctor, /adoc|asc(iidoc)?/, ["AsciiDoc"]) do |filename, content|
+  attributes = {
+    'showtitle' => '@',
+    'idprefix' => '',
+    'idseparator' => '-',
+    'docname' => File.basename(filename, (extname = File.extname(filename))),
+    'docfilesuffix' => extname,
+    'outfilesuffix' => extname,
+    'env' => 'github',
+    'env-github' => '',
+    'source-highlighter' => 'html-pipeline'
+  }
   Asciidoctor::Compliance.unique_id_start_index = 1
-  Asciidoctor.convert(content, :safe => :secure, :attributes => %w(showtitle=@ idprefix idseparator=- outfilesuffix=.adoc env=github env-github source-highlighter=html-pipeline))
+  Asciidoctor.convert(content, :safe => :secure, :attributes => attributes)
 end
 
 command(

test/markups/README.asciidoc

@@ -7,7 +7,7 @@
 
 Refer to <<another-section>> or <<another-section-1>>.
 
-Navigate to <<another-document#,another document>>.
+Navigate from {docname}{outfilesuffix} to <<another-document#,another document>>.
 
 == Another Section
 

test/markups/README.asciidoc.html

@@ -16,7 +16,7 @@ <h2>First Section</h2>
 <p>Refer to <a href="#another-section">Another Section</a> or <a href="#another-section-1">Another Section</a>.</p>
 </div>
 <div>
-<p>Navigate to <a href="another-document.adoc">another document</a>.</p>
+<p>Navigate from README.asciidoc to <a href="another-document.asciidoc">another document</a>.</p>
 </div>
 </div>
 </div>