Refactored the rdoc task to include more files and use the PROJECT_NAME

Rakefile

@@ -67,12 +67,14 @@ namespace :spec do
   end
 end
 
-desc 'Generate documentation for the Budget plugin.'
+desc 'Generate documentation for the plugin.'
 Rake::RDocTask.new(:rdoc) do |rdoc|
   rdoc.rdoc_dir = 'doc'
-  rdoc.title    = 'Budget'
+  rdoc.title    = PROJECT_NAME
   rdoc.options << '--line-numbers' << '--inline-source'
-  rdoc.rdoc_files.include('README.markdown')
+  rdoc.rdoc_files.include('*.markdown')
+  rdoc.rdoc_files.include('*.rdoc')
+  rdoc.rdoc_files.include('*.txt')
   rdoc.rdoc_files.include('lib/**/*.rb')
   rdoc.rdoc_files.include('app/**/*.rb')
 end