issue #22 add rdoc rake task

Rakefile

@@ -1 +1,13 @@
-require "bundler/gem_tasks"
+# encoding: UTF-8
+
+require 'bundler/gem_tasks'
+require 'rdoc/task'
+
+desc 'Generate documentation for the Cybele gem.'
+Rake::RDocTask.new(:rdoc) do |rdoc|
+  rdoc.rdoc_dir = 'rdoc'
+  rdoc.title    = 'Cybele'
+  rdoc.options << '--line-numbers' << '--inline-source'
+  rdoc.rdoc_files.include('README.md')
+  rdoc.rdoc_files.include('lib/**/*.rb')
+end