Add default rake task, add .idea to .gitignore

Add a default rake task to Rakefile (The test task). This should fix errors when building with [Travis](http://travis-ci.org), such as ```/home/travis/build/benbalter/benbalter.github.com/Rakefile:11:in `block in <top (required)>'
Tasks: TOP => test```

Add .idea to the .gitignore file, to allow [JetBrains WebStorm](http://www.jetbrains.com/webstorm) and [JetBrains RubyMine](http://www.jetbrains.com/ruby) users to commit without having to delete
build files.