Build documentation

Rakefile

@@ -6,6 +6,7 @@
 require 'open3'
 require 'pathname'
 require 'rake/clean'
+require 'asciidoctor-pdf'
 
 STAGES = Dir.glob('boot/stage*')
   .collect { |stage| File.basename stage }
@@ -13,6 +14,7 @@ STAGES = Dir.glob('boot/stage*')
   .drop(1) # First assembly stage does not count.
 
 CLEAN.include 'build/boot', 'build/valid'
+CLEAN.include 'doc/*.pdf'
 
 def compile(*arguments)
   sh(ENV.fetch('CC', 'gcc'), '-fpie', '-g', *arguments)
@@ -126,3 +128,10 @@ file 'build/boot/stage1/cl' => ['build/boot/stage1', 'boot/stage1.s'] do |t|
 
   compile('-nostdlib', '-o', t.name, *source)
 end
+
+rule '.pdf' => '.adoc' do |t|
+  Asciidoctor.convert_file t.source, backend: 'pdf', safe: :safe
+end
+
+desc 'Generate documentation'
+task doc: 'doc/language.pdf'