add rake release

Rakefile

@@ -47,7 +47,14 @@ Rake::RDocTask.new do |rdoc|
 end
 
 if defined?(Gem)
-  task 'build' do
+  task :release => :build do
+    sh "git commit --allow-empty -a -m 'up to #{source_version}'"
+    sh "git tag v#{source_version}"
+    sh "git push origin master"
+    sh "gem push pkg/god-#{source_version}.gem"
+  end
+
+  task :build => 'god.gemspec' do
     sh 'mkdir -p pkg'
     sh 'gem build god.gemspec'
     sh 'mv *.gem pkg'