osx: only strip x86_64 symbols
revert 9e8b17013cf69a659268797d9f10069e26243792 since the problem seems to have disappeared in master
OSX: add app.codesign_for_development Rakefile variable to enable codesign during development (normally only done in release builds)
add support for spritekit atlas files
integrate Bundler
add convenient rake task with "gem" namespace which is contained in "bundler/gem_tasks"
add 'rake' gem into Gemfile because `bundle exec rake' cause a Gem::LoadError

If run `bundle exec rake' without `rake' gem, the following error is occurred.
% bundle exec rake
/Users/watson/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/bundler-1.3.5/lib/bundler/rubygems_integration.rb:214:in `block in replace_gem': rake is not part of the bundle. Add it to Gemfile. (Gem::LoadError)
	from /Users/watson/.rbenv/versions/2.0.0-p247/bin/rake:22:in `<main>'
add *.gem into .gitignore in gem template
add Gemfile into gem template