Refactored, now using xcrun, input/output now in tmp files

Among the following changes, I also upped the package.json version and added the following details to the changelog file. This also fixes #1.

need to run "sudo xcode-select --switch /Applications/Xcode6-Beta.app/Contents/Developer/"
* Removed need for Xcode path
* Now using 'xcrun' command
* Input/Output now handled in temp folder/files
* No need to save .swift file before executing
* No file will be created in your project directory
* Keymap added
* Refactored plugin code