Add coverage task

Rakefile

@@ -27,6 +27,14 @@ RDoc::Task.new do |doc|
   doc.rdoc_files = FileList.new %w[lib/**/*.rb *.rdoc doc/rdoc/markup_reference.rb] - PARSER_FILES
 end
 
+task "coverage" do
+  cov = []
+  e = IO.popen([FileUtils::RUBY, "-I./lib", "exe/rdoc", "-C"], &:read)
+  e.scan(/^ *# in file (?<loc>.*)\n *(?<code>.*)|^ *(?<code>.*\S) *# in file (?<loc>.*)/) do
+    puts "%s: %s\n" % $~.values_at(:loc, :code)
+  end
+end
+
 Rake::TestTask.new(:normal_test) do |t|
   t.verbose = true
   t.deps = :generate