Take Advantage of ARC

This is a relatively minor PR that takes advantage of the semantics in ARC, since this project requires it. It also includes some minor formatting changes to make the code consistent.

* Uses `strong` or `copy` attributes instead of `retain`
* Doesn't check vars against nil or assign nil to vars on initialization
* Changes spacing of `if(var)` to `if (var)` in the places where the code isn't consistent.