Migrate documentation to LaTeX

Rakefile

@@ -4,16 +4,13 @@
 # frozen_string_literal: true
 
 require 'open3'
-require 'pathname'
 require 'rake/clean'
-require 'asciidoctor-pdf'
 
 STAGES = Dir.glob('boot/stage*')
   .collect { |stage| File.basename stage }
   .sort { |a, b| a.delete_prefix('stage').to_i <=> b.delete_prefix('stage').to_i }
   .drop(1) # First assembly stage does not count.
 
-CLEAN.include 'doc/*.pdf'
 CLOBBER.include 'build'
 
 def run(exe)
@@ -49,10 +46,3 @@ task :convert do
     end
   end
 end
-
-rule '.pdf' => '.adoc' do |t|
-  Asciidoctor.convert_file t.source, backend: 'pdf', safe: :safe
-end
-
-desc 'Generate documentation'
-task doc: 'doc/language.pdf'