Added support for --quiet

Added the ability for --quiet to be used to disable all stderr output if no error occurs while building the .dmg. Errors during the build will still be outputted. Updated help text. Changed package.json to version 0.3.0. No credit necessary.
![Preview](https://cloud.githubusercontent.com/assets/8171642/3791021/da0e22a2-1b24-11e4-9548-fe062fb33fbf.png)